设备树中ranges属性理解[通俗易懂]

大家好，又见面了，我是你们的朋友全栈君。

作者

彭东林
pengdonglin137@163.com

文章来源

http://www.cnblogs.com/pengdonglin137/p/7401049.html

正文

一、设备树

下面是我们将要实验的设备树的例子：

/ {
    #address-cells = <1>;
    #size-cells = <1>;

    demo_level0 {
        compatible = "simple-bus";
        ranges = <0x0 0x3000000 0x3000>;
        #address-cells = <1>;
        #size-cells = <1>;

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

        range@1 {
            compatible = "range";
            reg = <0x300 0x200>;
            reg-names = "range1";
        };

        range@2 {
            compatible = "range";
            reg = <0x600 0x200>;
            reg-names = "range2";
        };

        demo_level1 {
            compatible = "simple-bus";
            ranges = <0x0 0x1000 0x1000>;
            #address-cells = <1>;
            #size-cells = <1>;

            range@3 {
                compatible = "range";
                reg = <0x100 0x200>;
                reg-names = "range3";
            };

            demo_level1-1 {
                compatible = "simple-bus";
                ranges = <0x0 0x300 0x500>;
                #address-cells = <1>;
                #size-cells = <1>;

                range@4 {
                    compatible = "range";
                    reg = <0x100 0x200>;
                    reg-names = "range4";
                };

                range@5 {
                    compatible = "range";
                    reg = <0x300 0x100>;
                    reg-names = "range5";
                };

                demo_level1-1-1 {
                    compatible = "simple-bus";
                    ranges = <0x0 0x400 0x100>;
                    #address-cells = <1>;
                    #size-cells = <1>;

                    range@6 {
                        compatible = "range";
                        reg = <0x50 0x30>;
                        reg-names = "range6";
                    };

                    demo_level1-1-1-1 {
                        compatible = "simple-bus";
                        ranges = <0x0 0x20 0x20>;
                        #address-cells = <1>;
                        #size-cells = <1>;

                        range@7 {
                            compatible = "range";
                            reg = <0x10 0x10>;
                            reg-names = "range7";
                        };

                        range@8 {
                            compatible = "range";
                            reg = <0x0 0x10>;
                            reg-names = "range8";
                        };
                    };
                };
            };

            range@9 {
                compatible = "range";
                reg = <0x800 0x50>;
                reg-names = "range9";
            };

            demo_level1-2 {
                compatible = "simple-bus";
                ranges = <0x0 0x900 0x100>;
                #address-cells = <1>;
                #size-cells = <1>;

                range@10 {
                    compatible = "range";
                    reg = <0x0 0x50>;
                    reg-names = "range10";
                };

                demo_level1-2-1 {
                    compatible = "simple-bus";
                    ranges;
                    #address-cells = <1>;
                    #size-cells = <1>;

                    range@11 {
                        compatible = "range";
                        reg = <0x50 0x30>;
                        reg-names = "range11";
                    };
                };
            };
        };

        demo_level2 {
            compatible = "simple-bus";
            ranges;
            #address-cells = <1>;
            #size-cells = <1>;

            range@12 {
                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, 0);

    printk(KERN_INFO "%s start: 0x%x, end: 0x%x\n",
        res->name, res->start, res->end + 1);

    return 0;
}

static int demo_range_remove(struct platform_device *pdev)
{
    return 0;
}

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