ARM Linux 3.x 的设备树(Device Tree)之DTB、DTS

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1、ARM Device Tree起源

Linus Torvalds在2011年3月17日的ARM Linux邮件列表宣称“this whole ARM thing is a f*cking pain in the ass”,引发ARM Linux社区的地震,随后ARM社区进行了一系列的重大修正。在过去的ARM Linux中,arch/arm/plat-xxx和arch/arm/mach-xxx中充斥着大量的垃圾代码,相当多数的代码只是在描述板级细节,而这些板级细节对于内核来讲,不过是垃圾,如板上的platform设备、resource、i2c_board_info、spi_board_info以及各种硬件的platform_data。读者有兴趣可以统计下常见的s3c2410、s3c6410等板级目录,代码量在数万行。 

社区必须改变这种局面,于是PowerPC等其他体系架构下已经使用的Flattened Device Tree(FDT)进入ARM社区的视野。Device Tree是一种描述硬件的数据结构,它起源于 OpenFirmware (OF)。在Linux 2.6中,ARM架构的板极硬件细节过多地被硬编码在arch/arm/plat-xxx和arch/arm/mach-xxx,采用Device Tree后,许多硬件的细节可以直接透过它传递给Linux,而不再需要在kernel中进行大量的冗余编码。 

Device Tree由一系列被命名的结点(node)和属性(property)组成,而结点本身可包含子结点。所谓属性,其实就是成对出现的name和value。在Device Tree中,可描述的信息包括(原先这些信息大多被hard code到kernel中):

CPU的数量和类别 

内存基地址和大小 

总线和桥 

外设连接 

中断控制器和中断使用情况 

GPIO控制器和GPIO使用情况 

Clock控制器和Clock使用情况

它基本上就是画一棵电路板上CPU、总线、设备组成的树,Bootloader会将这棵树传递给内核,然后内核可以识别这棵树,并根据它展开出Linux内核中的platform_device、i2c_client、spi_device等设备,而这些设备用到的内存、IRQ等资源,也被传递给了内核,内核会将这些资源绑定给展开的相应的设备。

2、Device Tree组成和结构

整个Device Tree牵涉面比较广,即增加了新的用于描述设备硬件信息的文本格式,又增加了编译这一文本的工具,同时Bootloader也需要支持将编译后的Device Tree传递给Linux内核。 

DTS (device tree source) 

.dts文件是一种ASCII 文本格式的Device Tree描述,此文本格式非常人性化,适合人类的阅读习惯。基本上,在ARM Linux在,一个.dts文件对应一个ARM的machine,一般放置在内核的arch/arm/boot/dts/目录。由于一个SoC可能对应多个machine(一个SoC可以对应多个产品和电路板),势必这些.dts文件需包含许多共同的部分,Linux内核为了简化,把SoC公用的部分或者多个machine共同的部分一般提炼为.dtsi,类似于C语言的头文件。其他的machine对应的.dts就include这个.dtsi。譬如,对于VEXPRESS而言,vexpress-v2m.dtsi就被vexpress-v2p-ca9.dts所引用,
vexpress-v2p-ca9.dts有如下一行: 

/include/ “vexpress-v2m.dtsi” 

当然,和C语言的头文件类似,.dtsi也可以include其他的.dtsi,譬如几乎所有的ARM SoC的.dtsi都引用了skeleton.dtsi。 

.dts(或者其include的.dtsi)基本元素即为前文所述的结点和属性:

<code class="hljs applescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">/ {
    node1 {
        a-<span class="hljs-type" style="box-sizing: border-box;">string</span>-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"A string"</span>;
        a-<span class="hljs-type" style="box-sizing: border-box;">string</span>-<span class="hljs-type" style="box-sizing: border-box;">list</span>-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"first string"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"second string"</span>;
        a-byte-data-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x01</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x23</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x34</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x56</span>];
        child-node1 {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">first</span>-child-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span>;
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">second</span>-child-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>>;
            a-<span class="hljs-type" style="box-sizing: border-box;">string</span>-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hello, world"</span>;
        };
        child-node2 {
        };
    };
    node2 {
        an-empty-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span>;
        a-cell-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>>; /* each <span class="hljs-type" style="box-sizing: border-box;">number</span> (cell) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> a uint32 */
        child-node1 {
        };
    };
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>

上述.dts文件并没有什么真实的用途,但它基本表征了一个Device Tree源文件的结构: 

1个root结点”/”; 

root结点下面含一系列子结点,本例中为”node1” 和 “node2”; 

结点”node1”下又含有一系列子结点,本例中为”child-node1” 和 “child-node2”; 

各结点都有一系列属性。这些属性可能为空,如” an-empty-property”;可能为字符串,如”a-string-property”;可能为字符串数组,如”a-string-list-property”;可能为Cells(由u32整数组成),如”second-child-property”,可能为二进制数,如”a-byte-data-property”。 

下面以一个最简单的machine为例来看如何写一个.dts文件。假设此machine的配置如下: 

1个双核ARM Cortex-A9 32位处理器; 

ARM的local bus上的内存映射区域分布了2个串口(分别位于0x101F1000 和 0x101F2000)、GPIO控制器(位于0x101F3000)、SPI控制器(位于0x10170000)、中断控制器(位于0x10140000)和一个external bus桥; 

External bus桥上又连接了SMC SMC91111 Ethernet(位于0x10100000)、I2C控制器(位于0x10160000)、64MB NOR Flash(位于0x30000000); 

External bus桥上连接的I2C控制器所对应的I2C总线上又连接了Maxim DS1338实时钟(I2C地址为0x58)。 

其对应的.dts文件为:

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">/</span> {
    compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,coyotes-revenge"</span>;
    <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
    <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
    interrupt<span class="hljs-attribute" style="box-sizing: border-box;">-parent</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><&</span>intc<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;

    cpus {
        <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        cpu@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
            compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,cortex-a9"</span>;
            reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        };
        cpu@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> {
            compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,cortex-a9"</span>;
            reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        };
    };

    serial@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span>f0000 {
        compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl011"</span>;
        reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f0000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
    };

    serial@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span>f2000 {
        compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl011"</span>;
        reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f2000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
    };

    gpio@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span>f3000 {
        compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl061"</span>;
        reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f3000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span>
               <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f4000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0010</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
    };

    intc: interrupt<span class="hljs-attribute" style="box-sizing: border-box;">-controller</span>@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10140000</span> {
        compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl190"</span>;
        reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10140000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        interrupt<span class="hljs-attribute" style="box-sizing: border-box;">-controller</span>;
        <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#interrupt</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
    };

    spi@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10115000</span> {
        compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl022"</span>;
        reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10115000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
    };

    external<span class="hljs-attribute" style="box-sizing: border-box;">-bus</span> {
        <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>
        <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        ranges <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10100000</span>   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span>     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 1, Ethernet</span>
                  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10160000</span>   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span>     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 2, i2c controller</span>
                  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x30000000</span>   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 3, NOR Flash</span>

        ethernet@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
            compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"smc,smc91c111"</span>;
            reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
            interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        };

        i2c@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
            compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,a1234-i2c-bus"</span>;
            <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
            <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
            reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
            interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
            rtc@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58</span> {
                compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"maxim,ds1338"</span>;
                reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
                interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
            };
        };

        flash@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
            compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,k8f1315ebm"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"cfi-flash"</span>;
            reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x4000000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
        };
    };
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li></ul>

上述.dts文件中,root结点”/”的compatible 属性compatible = “acme,coyotes-revenge”;定义了系统的名称,它的组织形式为:,。Linux内核透过root结点”/”的compatible 属性即可判断它启动的是什么machine。 

在.dts文件的每个设备,都有一个compatible 属性,compatible属性用户驱动和设备的绑定。compatible 属性是一个字符串的列表,列表中的第一个字符串表征了结点代表的确切设备,形式为”,”,其后的字符串表征可兼容的其他设备。可以说前面的是特指,后面的则涵盖更广的范围。如在arch/arm/boot/dts/vexpress-v2m.dtsi中的Flash结点:

<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">flash<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@0</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">00000000</span> {
     compatible = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,vexpress-flash"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"cfi-flash"</span>;
     reg = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x00000000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x04000000</span>>,
     <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x00000000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x04000000</span>>;
     bank-width = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>>;
 };</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

compatible属性的第2个字符串”cfi-flash”明显比第1个字符串”arm,vexpress-flash”涵盖的范围更广。 

再比如,Freescale MPC8349 SoC含一个串口设备,它实现了国家半导体(National Semiconductor)的ns16550 寄存器接口。则MPC8349串口设备的compatible属性为compatible = “fsl,mpc8349-uart”, “ns16550”。其中,fsl,mpc8349-uart指代了确切的设备, ns16550代表该设备与National Semiconductor 的16550 UART保持了寄存器兼容。 

接下来root结点”/”的cpus子结点下面又包含2个cpu子结点,描述了此machine上的2个CPU,并且二者的compatible 属性为”arm,cortex-a9”。 

注意cpus和cpus的2个cpu子结点的命名,它们遵循的组织形式为:[@],<>中的内容是必选项,[]中的则为可选项。name是一个ASCII字符串,用于描述结点对应的设备类型,如3com Ethernet适配器对应的结点name宜为ethernet,而不是3com509。如果一个结点描述的设备有地址,则应该给出@unit-address。多个相同类型设备结点的name可以一样,只要unit-address不同即可,如本例中含有cpu@0、cpu@1以及serial@101f0000与serial@101f2000这样的同名结点。设备的unit-address地址也经常在其对应结点的reg属性中给出。ePAPR标准给出了结点命名的规范。 

可寻址的设备使用如下信息来在Device Tree中编码地址信息: 

reg 

#address-cells 

#size-cells 

其中reg的组织形式为reg =

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> ranges = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10100000</span>   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span>     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 1, Ethernet</span>
 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10160000</span>   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span>     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 2, i2c controller</span>
 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>  <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x30000000</span>   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000000</span>>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 3, NOR Flash</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

ranges是地址转换表,其中的每个项目是一个子地址、父地址以及在子地址空间的大小的映射。映射表中的子地址、父地址分别采用子地址空间的#address-cells和父地址空间的#address-cells大小。对于本例而言,子地址空间的#address-cells为2,父地址空间的#address-cells值为1,因此0 0 0x10100000 0x10000的前2个cell为external-bus后片选0上偏移0,第3个cell表示external-bus后片选0上偏移0的地址空间被映射到CPU的0x10100000位置,第4个cell表示映射的大小为0x10000。ranges的后面2个项目的含义可以类推。

Device Tree中还可以中断连接信息,对于中断控制器而言,它提供如下属性:

interrupt-controller – 这个属性为空,中断控制器应该加上此属性表明自己的身份;

interrupt-cells – 与#address-cells 和 #size-cells相似,它表明连接此中断控制器的设备的interrupts属性的cell大小。 

在整个Device Tree中,与中断相关的属性还包括:

interrupt-parent – 设备结点透过它来指定它所依附的中断控制器的phandle,当结点没有指定interrupt-parent 时,则从父级结点继承。对于本例而言,root结点指定了interrupt-parent = <&intc>;其对应于intc: interrupt-controller@10140000,而root结点的子结点并未指定interrupt-parent,因此它们都继承了intc,即位于0x10140000的中断控制器。

interrupts – 用到了中断的设备结点透过它指定中断号、触发方法等,具体这个属性含有多少个cell,由它依附的中断控制器结点的#interrupt-cells属性决定。而具体每个cell又是什么含义,一般由驱动的实现决定,而且也会在Device Tree的binding文档中说明。譬如,对于ARM GIC中断控制器而言,#interrupt-cells为3,它3个cell的具体含义Documentation/devicetree/bindings/arm/gic.txt就有如下文字说明:

<code class="hljs applescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">01</span>   The <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>st cell <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt type; <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> SPI interrupts, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> PPI
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">02</span>   interrupts.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">04</span>   The <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>nd cell <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">contains</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt <span class="hljs-type" style="box-sizing: border-box;">number</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt type.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">05</span>   SPI interrupts are <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> range [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">987</span>].  PPI interrupts are <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span>   range [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span>].
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">07</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">08</span>   The <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>rd cell <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> flags, encoded <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">as</span> follows:
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">09</span>         bits[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] trigger type <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> level flags.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>                 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> = low-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span>-high edge triggered
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>                 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> = high-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span>-low edge triggered
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">12</span>                 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span> = active high level-sensitive
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">13</span>                 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span> = active low level-sensitive
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span>         bits[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>] PPI interrupt cpu mask.  Each bit corresponds <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> each <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span> possible cpus attached <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> GIC.  A bit <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> '<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>' indicated
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">16</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> wired <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">that</span> CPU.  Only valid <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> PPI interrupts.</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

另外,值得注意的是,一个设备还可能用到多个中断号。对于ARM GIC而言,若某设备使用了SPI的168、169号2个中断,而言都是高电平触发,则该设备结点的interrupts属性可定义为:interrupts = <0 168 4>, <0 169 4>; 

除了中断以外,在ARM Linux中clock、GPIO、pinmux都可以透过.dts中的结点和属性进行描述。

3、DTC (device tree compiler)

将.dts编译为.dtb的工具。DTC的源代码位于内核的scripts/dtc目录,在Linux内核使能了Device Tree的情况下,编译内核的时候主机工具dtc会被编译出来,对应scripts/dtc/Makefile中的“hostprogs-y := dtc”这一hostprogs编译target。 

在Linux内核的arch/arm/boot/dts/Makefile中,描述了当某种SoC被选中后,哪些.dtb文件会被编译出来,如与VEXPRESS对应的.dtb包括:

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">dtb<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-</span>$(CONFIG_ARCH_VEXPRESS) <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">+=</span> vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca5s</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"></span>
        vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca9</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"></span>
        vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca15</span><span class="hljs-attribute" style="box-sizing: border-box;">-tc1</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"></span>
        vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca15_a7</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"></span>
        xenvm<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4.2</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

在Linux下,我们可以单独编译Device Tree文件。当我们在Linux内核下运行make dtbs时,若我们之前选择了ARCH_VEXPRESS,上述.dtb都会由对应的.dts编译出来。因为arch/arm/Makefile中含有一个dtbs编译target项目。

4、Device Tree Blob (.dtb)

.dtb是.dts被DTC编译后的二进制格式的Device Tree描述,可由Linux内核解析。通常在我们为电路板制作NAND、SD启动image时,会为.dtb文件单独留下一个很小的区域以存放之,之后bootloader在引导kernel的过程中,会先读取该.dtb到内存。 

Binding 

对于Device Tree中的结点和属性具体是如何来描述设备的硬件细节的,一般需要文档来进行讲解,文档的后缀名一般为.txt。这些文档位于内核的Documentation/devicetree/bindings目录,其下又分为很多子目录。

5、Bootloader

Uboot mainline 从 v1.1.3开始支持Device Tree,其对ARM的支持则是和ARM内核支持Device Tree同期完成。 

为了使能Device Tree,需要编译Uboot的时候在config文件中加入#define CONFIG_OF_LIBFDT

在Uboot中,可以从NAND、SD或者TFTP等任意介质将.dtb读入内存,假设.dtb放入的内存地址为0x71000000,之后可在Uboot运行命令fdt addr命令设置.dtb的地址,如: 

U-Boot> fdt addr 0x71000000 

fdt的其他命令就变地可以使用,如fdt resize、fdt print等。 

对于ARM来讲,可以透过bootz kernel_addr initrd_address dtb_address的命令来启动内核,即dtb_address作为bootz或者bootm的最后一次参数,第一个参数为内核映像的地址,第二个参数为initrd的地址,若不存在initrd,可以用 -代替。

6、Device Tree引发的BSP和驱动变更

有了Device Tree后,大量的板级信息都不再需要,譬如过去经常在arch/arm/plat-xxx和arch/arm/mach-xxx实施的如下事情: 

1. 注册platform_device,绑定resource,即内存、IRQ等板级信息。 

透过Device Tree后,形如

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">90</span> static struct resource xxx_resources[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">91</span>         [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">92</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span>  = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">93</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.end</span>    = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">94</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.flags</span>  = IORESOURCE_MEM,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">95</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">96</span>         [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">97</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span>  = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">98</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.end</span>    = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">99</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.flags</span>  = IORESOURCE_IRQ,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">102</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">103</span> static struct platform_device xxx_device = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">104</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span>           = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"xxx"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">105</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.id</span>             = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">106</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dev</span>            = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">107</span>                                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.platform</span>_data          = &xxx_data,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">108</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">109</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.resource</span>       = xxx_resources,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">110</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.num</span>_resources  = ARRAY_SIZE(xxx_resources),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">111</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li></ul>

之类的platform_device代码都不再需要,其中platform_device会由kernel自动展开。而这些resource实际来源于.dts中设备结点的reg、interrupts属性。典型地,大多数总线都与“simple_bus”兼容,而在SoC对应的machine的.init_machine成员函数中,调用of_platform_bus_probe(NULL, xxx_of_bus_ids, NULL);即可自动展开所有的platform_device。譬如,假设我们有个XXX SoC,则可在arch/arm/mach-xxx/的板文件中透过如下方式展开.dts中的设备结点对应的platform_device:

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">18</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> of_device_id xxx_of_bus_ids[] __initdata = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">19</span>         { <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.compatible</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"simple-bus"</span>, },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span>         {},
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span> };
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">23</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> __init xxx_mach_init(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">24</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">25</span>         of_platform_bus_probe(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>, xxx_of_bus_ids, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">26</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">33</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#ifdef CONFIG_ARCH_XXX</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">38</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">39</span> DT_MACHINE_START(XXX_DT, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Generic XXX (Flattened Device Tree)"</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">41</span>         …
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">45</span>         <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.init_machine</span>   = xxx_mach_init,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">46</span>         …
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">49</span> MACHINE_END
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#endif</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>
  1. 注册i2c_board_info,指定IRQ等板级信息。 

    形如
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">145</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> i2c_board_info __initdata afeb9260_i2c_devices[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">146</span>         {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">147</span>                 I2C_BOARD_INFO(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tlv320aic23"</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1a</span>),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">148</span>         }, {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">149</span>                 I2C_BOARD_INFO(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fm3130"</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x68</span>),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">150</span>         }, {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">151</span>                 I2C_BOARD_INFO(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"24c64"</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x50</span>),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">152</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">153</span> };</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

之类的i2c_board_info代码,目前不再需要出现,现在只需要把tlv320aic23、fm3130、24c64这些设备结点填充作为相应的I2C controller结点的子结点即可,类似于前面的

<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">      i2c<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
            compatible = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,a1234-i2c-bus"</span>;
            …
            rtc<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@58</span> {
                compatible = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"maxim,ds1338"</span>;
                reg = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58</span>>;
                interrupts = < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> >;
            };
        };</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

Device Tree中的I2C client会透过I2C host驱动的probe()函数中调用of_i2c_register_devices(&i2c_dev->adapter);被自动展开。 

3. 注册spi_board_info,指定IRQ等板级信息。 

形如

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">79</span> static struct spi_board_info afeb9260_spi_devices[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span>         {       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* DataFlash chip */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">81</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.modalias</span>       = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"mtd_dataflash"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">82</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.chip</span>_select    = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">83</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.max</span>_speed_hz   = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">84</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.bus</span>_num        = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">85</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">86</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

之类的spi_board_info代码,目前不再需要出现,与I2C类似,现在只需要把mtd_dataflash之类的结点,作为SPI控制器的子结点即可,SPI host驱动的probe函数透过spi_register_master()注册master的时候,会自动展开依附于它的slave。 

4. 多个针对不同电路板的machine,以及相关的callback。 

过去,ARM Linux针对不同的电路板会建立由MACHINE_START和MACHINE_END包围起来的针对这个machine的一系列callback,譬如:

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">373</span> MACHINE_START(VEXPRESS, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ARM-Versatile Express"</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">374</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.atag</span>_offset    = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x100</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">375</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.smp</span>            = smp_ops(vexpress_smp_ops),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">376</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>_io         = v2m_map_io,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">377</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_early     = v2m_init_early,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">378</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_irq       = v2m_init_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">379</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.timer</span>          = &v2m_timer,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">380</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.handle</span>_irq     = gic_handle_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">381</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_machine   = v2m_init,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">382</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.restart</span>        = vexpress_restart,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">383</span> MACHINE_END</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

这些不同的machine会有不同的MACHINE ID,Uboot在启动Linux内核时会将MACHINE ID存放在r1寄存器,Linux启动时会匹配Bootloader传递的MACHINE ID和MACHINE_START声明的MACHINE ID,然后执行相应machine的一系列初始化函数。 

引入Device Tree之后,MACHINE_START变更为DT_MACHINE_START,其中含有一个.dt_compat成员,用于表明相关的machine与.dts中root结点的compatible属性兼容关系。如果Bootloader传递给内核的Device Tree中root结点的compatible属性出现在某machine的.dt_compat表中,相关的machine就与对应的Device Tree匹配,从而引发这一machine的一系列初始化函数被执行。

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">489</span> static const char * const v2m_dt_match[] __initconst = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">490</span>         <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,vexpress"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">491</span>         <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"xen,xenvm"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">492</span>         NULL,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">493</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">495</span> DT_MACHINE_START(VEXPRESS_DT, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ARM-Versatile Express"</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">496</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dt</span>_compat      = v2m_dt_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">497</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.smp</span>            = smp_ops(vexpress_smp_ops),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">498</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>_io         = v2m_dt_map_io,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">499</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_early     = v2m_dt_init_early,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">500</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_irq       = v2m_dt_init_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">501</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.timer</span>          = &v2m_dt_timer,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">502</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_machine   = v2m_dt_init,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">503</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.handle</span>_irq     = gic_handle_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">504</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.restart</span>        = vexpress_restart,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">505</span> MACHINE_END</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

Linux倡导针对多个SoC、多个电路板的通用DT machine,即一个DT machine的.dt_compat表含多个电路板.dts文件的root结点compatible属性字符串。之后,如果的电路板的初始化序列不一样,可以透过int of_machine_is_compatible(const char *compat) API判断具体的电路板是什么。 

譬如arch/arm/mach-exynos/mach-exynos5-dt.c的EXYNOS5_DT machine同时兼容”samsung,exynos5250”和”samsung,exynos5440”:

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">158</span> static char const *exynos5_dt_compat[] __initdata = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">159</span>         <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5250"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">160</span>         <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5440"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">161</span>         NULL
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">162</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">163</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">177</span> DT_MACHINE_START(EXYNOS5_DT, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"SAMSUNG EXYNOS5 (Flattened Device Tree)"</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">178</span>         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* Maintainer: Kukjin Kim <kgene.kim@samsung.com> */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">179</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_irq       = exynos5_init_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">180</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.smp</span>            = smp_ops(exynos_smp_ops),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">181</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>_io         = exynos5_dt_map_io,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">182</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.handle</span>_irq     = gic_handle_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">183</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_machine   = exynos5_dt_machine_init,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">184</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_late      = exynos_init_late,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">185</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.timer</span>          = &exynos4_timer,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">186</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dt</span>_compat      = exynos5_dt_compat,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">187</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.restart</span>        = exynos5_restart,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">188</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.reserve</span>        = exynos5_reserve,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">189</span> MACHINE_END</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>

它的.init_machine成员函数就针对不同的machine进行了不同的分支处理:

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">126</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> __init exynos5_dt_machine_init(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">127</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">128</span>         …
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">149</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">150</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_machine_is_compatible(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5250"</span>))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">151</span>                 of_platform_populate(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>, of_default_bus_match_table,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">152</span>                                      exynos5250_auxdata_lookup, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">153</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_machine_is_compatible(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5440"</span>))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">154</span>                 of_platform_populate(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>, of_default_bus_match_table,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">155</span>                                      exynos5440_auxdata_lookup, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">156</span> }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

使用Device Tree后,驱动需要与.dts中描述的设备结点进行匹配,从而引发驱动的probe()函数执行。对于platform_driver而言,需要添加一个OF匹配表,如前文的.dts文件的”acme,a1234-i2c-bus”兼容I2C控制器结点的OF匹配表可以是:

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">436</span> static const struct of_device_id a1234_i2c_of_match[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">437</span>         { <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.compatible</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,a1234-i2c-bus "</span>, },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">438</span>         {},
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">439</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">440</span> MODULE_DEVICE_TABLE(of, a1234_i2c_of_match)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">441</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">442</span> static struct platform_driver i2c_a1234_driver = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">443</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.driver</span> = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">444</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"a1234-i2c-bus "</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">445</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.owner</span> = THIS_MODULE,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">449</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.of</span>_match_table = a1234_i2c_of_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">450</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">451</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.probe</span> = i2c_a1234_probe,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">452</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.remove</span> = i2c_a1234_remove,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">453</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">454</span> module_platform_driver(i2c_a1234_driver)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

对于I2C和SPI从设备而言,同样也可以透过of_match_table添加匹配的.dts中的相关结点的compatible属性,如sound/soc/codecs/wm8753.c中的:

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1533</span> static const struct of_device_id wm8753_of_match[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1534</span>         { <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.compatible</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wlf,wm8753"</span>, },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1535</span>         { }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1536</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1537</span> MODULE_DEVICE_TABLE(of, wm8753_of_match)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1587</span> static struct spi_driver wm8753_spi_driver = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1588</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.driver</span> = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1589</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span>   = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wm8753"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1590</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.owner</span>  = THIS_MODULE,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1591</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.of</span>_match_table = wm8753_of_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1592</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1593</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.probe</span>          = wm8753_spi_probe,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1594</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.remove</span>         = wm8753_spi_remove,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1595</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1640</span> static struct i2c_driver wm8753_i2c_driver = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1641</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.driver</span> = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1642</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wm8753"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1643</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.owner</span> = THIS_MODULE,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1644</span>                 <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.of</span>_match_table = wm8753_of_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1645</span>         },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1646</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.probe</span> =    wm8753_i2c_probe,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1647</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.remove</span> =   wm8753_i2c_remove,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1648</span>         <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.id</span>_table = wm8753_i2c_id,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1649</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>

不过这边有一点需要提醒的是,I2C和SPI外设驱动和Device Tree中设备结点的compatible 属性还有一种弱式匹配方法,就是别名匹配。compatible 属性的组织形式为,,别名其实就是去掉compatible 属性中逗号前的manufacturer前缀。关于这一点,可查看drivers/spi/spi.c的源代码,函数spi_match_device()暴露了更多的细节,如果别名出现在设备spi_driver的id_table里面,或者别名与spi_driver的name字段相同,SPI设备和驱动都可以匹配上:

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">90</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> spi_match_device(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device *dev, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_driver *drv)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">91</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">92</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device *spi = to_spi_device(dev);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">93</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_driver *sdrv = to_spi_driver(drv);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">94</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">95</span>         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* Attempt an OF style match */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">96</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_driver_match_device(dev, drv))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">97</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">98</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">99</span>         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* Then try ACPI */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (acpi_driver_match_device(dev, drv))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">102</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">103</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (sdrv->id_table)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">104</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> !!spi_match_id(sdrv->id_table, spi);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">105</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">106</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> strcmp(spi->modalias, drv->name) == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">107</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">71</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device_id *spi_match_id(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device_id *<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">72</span>                                                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device *sdev)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">73</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">74</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>->name[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]) {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">75</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!strcmp(sdev->modalias, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>->name))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">76</span>                         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">77</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>++;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">78</span>         }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">79</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span> }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>

7、 常用OF API

在Linux的BSP和驱动代码中,还经常会使用到Linux中一组Device Tree的API,这些API通常被冠以of_前缀,它们的实现代码位于内核的drivers/of目录。这些常用的API包括: 

int of_device_is_compatible(const struct device_node *device,const char *compat); 

判断设备结点的compatible 属性是否包含compat指定的字符串。当一个驱动支持2个或多个设备的时候,这些不同.dts文件中设备的compatible 属性都会进入驱动 OF匹配表。因此驱动可以透过Bootloader传递给内核的Device Tree中的真正结点的compatible 属性以确定究竟是哪一种设备,从而根据不同的设备类型进行不同的处理。如drivers/pinctrl/pinctrl-sirf.c即兼容于”sirf,prima2-pinctrl”,又兼容于”sirf,prima2-pinctrl”,在驱动中就有相应分支处理:

<code class="hljs bash has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1682</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_device_is_compatible(np, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"sirf,marco-pinctrl"</span>))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1683</span>      is_marco = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

struct device_node *of_find_compatible_node(struct device_node *from, 

const char *type, const char *compatible); 

根据compatible属性,获得设备结点。遍历Device Tree中所有的设备结点,看看哪个结点的类型、compatible属性与本函数的输入参数匹配,大多数情况下,from、type为NULL。 

int of_property_read_u8_array(const struct device_node *np, 

const char *propname, u8 *out_values, size_t sz); 

int of_property_read_u16_array(const struct device_node *np, 

const char *propname, u16 *out_values, size_t sz); 

int of_property_read_u32_array(const struct device_node *np, 

const char *propname, u32 *out_values, size_t sz); 

int of_property_read_u64(const struct device_node *np, const char 

*propname, u64 *out_value); 

读取设备结点np的属性名为propname,类型为8、16、32、64位整型数组的属性。对于32位处理器来讲,最常用的是of_property_read_u32_array()。如在arch/arm/mm/cache-l2x0.c中,透过如下语句读取L2 cache的”arm,data-latency”属性:

<code class="hljs haskell has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">534</span>         of_property_read_u32_array(np, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,data-latency"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">535</span>                                    <span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>, <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">ARRAY_SIZE</span><span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-title" style="box-sizing: border-box;">data</span>)</span>);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

在arch/arm/boot/dts/vexpress-v2p-ca9.dts中,含有”arm,data-latency”属性的L2 cache结点如下:

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">137</span>         L2: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">cache</span><span class="hljs-attribute" style="box-sizing: border-box;">-controller</span>@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1e00</span>a000 {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">138</span>                 compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl310-cache"</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">139</span>                 reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1e00a000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">140</span>                 interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">43</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">141</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">cache</span><span class="hljs-attribute" style="box-sizing: border-box;">-level</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">142</span>                 arm,<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span><span class="hljs-attribute" style="box-sizing: border-box;">-latency</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">143</span>                 arm,<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">tag</span><span class="hljs-attribute" style="box-sizing: border-box;">-latency</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">144</span>         }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

有些情况下,整形属性的长度可能为1,于是内核为了方便调用者,又在上述API的基础上封装出了更加简单的读单一整形属性的API,它们为int of_property_read_u8()、of_property_read_u16()等,实现于include/linux/of.h:

<code class="hljs rust has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">513</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> inline <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> of_property_read_u8(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">514</span>                                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *propname,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">515</span>                                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">u8</span> *out_value)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">516</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">517</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> of_property_read_u8_array(np, propname, out_value, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">518</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">519</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">520</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> inline <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> of_property_read_u16(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">521</span>                                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *propname,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">522</span>                                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">u16</span> *out_value)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">523</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">524</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> of_property_read_u16_array(np, propname, out_value, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">525</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">526</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">527</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> inline <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> of_property_read_u32(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">528</span>                                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *propname,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">529</span>                                        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">u32</span> *out_value)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">530</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">531</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> of_property_read_u32_array(np, propname, out_value, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">532</span> }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>

int of_property_read_string(struct device_node *np, const char 

*propname, const char **out_string); 

int of_property_read_string_index(struct device_node *np, const char 

*propname, int index, const char **output); 

前者读取字符串属性,后者读取字符串数组属性中的第index个字符串。如drivers/clk/clk.c中的of_clk_get_parent_name()透过of_property_read_string_index()遍历clkspec结点的所有”clock-output-names”字符串数组属性。

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1759</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *of_clk_get_parent_name(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> index)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1760</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1761</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> of_phandle_args clkspec;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1762</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *clk_name;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1763</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> rc;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1764</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1765</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (index < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1766</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1767</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1768</span>         rc = of_parse_phandle_with_args(np, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"clocks"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"#clock-cells"</span>, index,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1769</span>                                         &clkspec);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1770</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (rc)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1771</span>                 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1772</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1773</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_property_read_string_index(clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.np</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"clock-output-names"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1774</span>                                   clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.args_count</span> ? clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.args</span>[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] : <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1775</span>                                           &clk_name) < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1776</span>                 clk_name = clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.np</span>->name;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1777</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1778</span>         of_node_put(clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.np</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1779</span>         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> clk_name;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1780</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1781</span> EXPORT_SYMBOL_GPL(of_clk_get_parent_name);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>

static inline bool of_property_read_bool(const struct device_node *np, 

const char *propname); 

如果设备结点np含有propname属性,则返回true,否则返回false。一般用于检查空属性是否存在。

void __iomem *of_iomap(struct device_node *node, int index); 

通过设备结点直接进行设备内存区间的 ioremap(),index是内存段的索引。若设备结点的reg属性有多段,可通过index标示要ioremap的是哪一段,只有1段的情况,index为0。采用Device Tree后,大量的设备驱动通过of_iomap()进行映射,而不再通过传统的ioremap。

unsigned int irq_of_parse_and_map(struct device_node *dev, int index); 

透过Device Tree或者设备的中断号,实际上是从.dts中的interrupts属性解析出中断号。若设备使用了多个中断,index指定中断的索引号。 

还有一些OF API,这里不一一列举,具体可参考include/linux/of.h头文件。

8、总结

ARM社区一贯充斥的大量垃圾代码导致Linus盛怒,因此社区在2011年到2012年进行了大量的工作。ARM Linux开始围绕Device Tree展开,Device Tree有自己的独立的语法,它的源文件为.dts,编译后得到.dtb,Bootloader在引导Linux内核的时候会将.dtb地址告知内核。之后内核会展开Device Tree并创建和注册相关的设备,因此arch/arm/mach-xxx和arch/arm/plat-xxx中大量的用于注册platform、I2C、SPI板级信息的代码被删除,而驱动也以新的方式和.dts中定义的设备结点进行匹配。