设备树中ranges属性分析（1）

作者

彭东林

pengdonglin137@163.com

 

软件环境

Linux-4.10.17

Qemu+vexpress

 

概述

在设备树中有时会看到ranges属性，这个ranges属性可以达到什么效果呢？ 今天看到宋宝华老师的设备树讲座，才知道。为了有一个直观的印象，下面我们结合一个实际的例子来看看

 

正文

一、设备树

下面是我们将要实验的设备树的例子：

 / {
     #address-cells = <>;
     #size-cells = <>;

     demo_level0 {
         compatible = "simple-bus";
         ranges = <0x0 0x3000000 0x3000>;
         #address-cells = <>;
         #size-cells = <>;

         range@ {
             compatible = "range";
             reg = <0x100 0x200>;
             reg-names = "range0";
         };

         range@ {
             compatible = "range";
             reg = <0x300 0x200>;
             reg-names = "range1";
         };

         range@ {
             compatible = "range";
             reg = <0x600 0x200>;
             reg-names = "range2";
         };

         demo_level1 {
             compatible = "simple-bus";
             ranges = <0x0 0x1000 0x1000>;
             #address-cells = <>;
             #size-cells = <>;

             range@ {
                 compatible = "range";
                 reg = <0x100 0x200>;
                 reg-names = "range3";
             };

             demo_level1- {
                 compatible = "simple-bus";
                 ranges = <0x0 0x300 0x500>;
                 #address-cells = <>;
                 #size-cells = <>;

                 range@ {
                     compatible = "range";
                     reg = <0x100 0x200>;
                     reg-names = "range4";
                 };

                 range@ {
                     compatible = "range";
                     reg = <0x300 0x100>;
                     reg-names = "range5";
                 };

                 demo_level1-- {
                     compatible = "simple-bus";
                     ranges = <0x0 0x400 0x100>;
                     #address-cells = <>;
                     #size-cells = <>;

                     range@ {
                         compatible = "range";
                         reg = <0x50 0x30>;
                         reg-names = "range6";
                     };

                     demo_level1--- {
                         compatible = "simple-bus";
                         ranges = <0x0 0x20 0x20>;
                         #address-cells = <>;
                         #size-cells = <>;

                         range@ {
                             compatible = "range";
                             reg = <0x10 0x10>;
                             reg-names = "range7";
                         };

                         range@ {
                             compatible = "range";
                             reg = <0x0 0x10>;
                             reg-names = "range8";
                         };
                     };
                 };
             };

             range@ {
                 compatible = "range";
                 reg = <0x800 0x50>;
                 reg-names = "range9";
             };

             demo_level1- {
                 compatible = "simple-bus";
                 ranges = <0x0 0x900 0x100>;
                 #address-cells = <>;
                 #size-cells = <>;

                 range@ {
                     compatible = "range";
                     reg = <0x0 0x50>;
                     reg-names = "range10";
                 };

                 demo_level1-- {
                     compatible = "simple-bus";
                     ranges;
                     #address-cells = <>;
                     #size-cells = <>;

                     range@ {
                         compatible = "range";
                         reg = <0x50 0x30>;
                         reg-names = "range11";
                     };
                 };
             };
         };

         demo_level2 {
             compatible = "simple-bus";
             ranges;
             #address-cells = <>;
             #size-cells = <>;

             range@ {
                 compatible = "range";
                 reg = <0x2000 0x1000>;
                 reg-names = "range12";
             };
         };
     }
 };

 

二、驱动

下面是一个简单的驱动，功能很简单，只是在probe函数中将memory资源的start和(end+1)打印出来.

demo_range.c:

#include <linux/init.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/of.h>

static int demo_range_probe(struct platform_device *pdev)
{
    struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, );

    printk(KERN_INFO "%s start: 0x%x, end: 0x%x\n",
        res->name, res->start, res->end + );

    return ;
}

static int demo_range_remove(struct platform_device *pdev)
{
    return ;
}

static const struct of_device_id demo_range_of_match[]  = {
    { .compatible = "range"},
    {},
};

static struct platform_driver demo_range_driver = {
    .driver = {
        .name = "demo_range",
        .owner = THIS_MODULE,
        .of_match_table = demo_range_of_match,
    },
    .probe = demo_range_probe,
    .remove = demo_range_remove,
};
module_platform_driver(demo_range_driver);

MODULE_LICENSE("GPL v2");

在驱动中会获得memory资源，然后将start和(end+1)打印出来，之所以这里用(end+1)，仅仅是为了便于理解下面的kernel log。

三、验证

编译驱动，然后加载，可以看到下面的打印信息：

[root@vexpress mnt]# insmod demo_range.ko
[  382.940402] range0 start: 0x3000100, end: 0x3000300
[  382.940697] range1 start: 0x3000300, end: 0x3000500
[  382.941448] range2 start: 0x3000600, end: 0x3000800
[  382.941657] range3 start: 0x3001100, end: 0x3001300
[  382.941855] range4 start: 0x3001400, end: 0x3001600
[  382.942057] range5 start: 0x3001600, end: 0x3001700
[  382.942262] range6 start: 0x3001750, end: 0x3001780
[  382.942470] range7 start: 0x3001730, end: 0x3001740
[  382.942684] range8 start: 0x3001720, end: 0x3001730
[  382.949796] range9 start: 0x3001800, end: 0x3001850
[  382.950023] range10 start: 0x3001900, end: 0x3001950
[  382.950603] range11 start: 0x3001950, end: 0x3001980
[  382.950805] range12 start: 0x3002000, end: 0x3003000

 

总结：

1、ranges属性值的格式 <local地址， parent地址， size>， 表示将local地址向parent地址的转换。

比如对于#address-cells和#size-cells都为1的话，以<0x0  0x10 0x20>为例，表示将local的从0x0~(0x0 + 0x20)的地址空间映射到parent的0x10~(0x10 + 0x20)

 

其中，local地址的个数取决于当前含有ranges属性的节点的#address-cells属性的值，size取决于当前含有ranges属性的节点的#size-cells属性的值。

而parent地址的个数取决于当前含有ranges属性的节点的parent节点的#address-cells的值。

 

2、对于含有ranges属性的节点的子节点来说，其reg都是基于local地址的

 

3、ranges属性值为空的话，表示1:1映射

 

4、对于没有ranges属性的节点，代表不是memory map区域

 

四、示意图

对照上面的log理解下面的框图

 

 

 

 

完。