1.什么是DTS？为什么要引入DTS？

DTS即Device Tree Source设备树源码,DeviceTree是一种描述硬件的数据结构，它起源于OpenFirmware (OF)。

在Linux2.6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，比如板上的platform设备、resource、i2c_board_info、spi_board_info以及各种硬件的platform_data，这些板级细节代码对内核来讲只不过是垃圾代码。而采用DeviceTree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。   

2.ARM平台的相关code做出如下相关规范调整

本质上，Device Tree改变了原来用hardcode方式将HW配置信息嵌入到内核代码的方法，改用bootloader传递一个DB的形式。

3.DTS的加载过程

4.DTS的描述信息

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DeviceTree中，可描述的信息包括（原先这些信息大多被hardcode到kernel中）：

  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。

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。所有的ARMSoC的.dtsi都引用了skeleton.dtsi，即#include"skeleton.dtsi“或者 /include/ "skeleton.dtsi"

5.变化

现在：

    interrupt_demo: interrupt_demo {
            compatible         = "tiny4412,interrupt_demo";
            tiny4412,int_gpio1 = <&gpx3 2 GPIO_ACTIVE_HIGH>;
            tiny4412,int_gpio2 = <&gpx3 3 GPIO_ACTIVE_HIGH>;
            tiny4412,int_gpio3 = <&gpx3 4 GPIO_ACTIVE_HIGH>;
            tiny4412,int_gpio4 = <&gpx3 5 GPIO_ACTIVE_HIGH>;
    };

2、完整的设备树文件：

/*
 * FriendlyARM's Exynos4412 based TINY4412 board device tree source
 *
 * Copyright (c) 2013 Alex Ling <kasimling@gmail.com>
 *
 * Device tree source file for FriendlyARM's TINY4412 board which is based on
 * Samsung's Exynos4412 SoC.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
*/

/dts-v1/;
#include "exynos4412.dtsi"
#include <dt-bindings/gpio/gpio.h>

/ {  //root结点"/"
	model = "FriendlyARM TINY4412 board based on Exynos4412";
	//root结点"/"的属性compatible，组织形式为：<manufacturer>,<model>
	//Linux内核透过root结点"/"的compatible 属性即可判断它启动的是什么machine
	//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"<manufacturer>,<model>"，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。
	compatible = "friendlyarm,tiny4412", "samsung,exynos4412", "samsung,exynos4";

  //以下开始为子节点
	//子结点的命名，它们遵循的组织形式为：<name>[@<unit-address>]，
	//<>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memory；
	//多个相同类型设备结点的name可以一样，只要unit-address不同即可
	
	//chosen节点并不代表一个真正的设备，而是用来在Firmware与操作系统间传递数据，如启动参数。
	chosen {                         //子结点"chosen"
		stdout-path = &serial_0;
		bootargs = "root=/dev/ram0 rw rootfstype=ext4 console=ttySAC0,115200 init=/linuxrc earlyprintk";
	};

	memory {                         //子结点"memory"
		reg = <0x40000000 0x40000000>;
	};

	leds {                           //子结点"leds"
		compatible = "gpio-leds";

		led1 {                         //子子结点"led1"
			label = "led1";
			gpios = <&gpm4 0 GPIO_ACTIVE_LOW>;
			default-state = "off";
			linux,default-trigger = "heartbeat";
		};

		led2 {
			label = "led2";
			gpios = <&gpm4 1 GPIO_ACTIVE_LOW>;
			default-state = "off";
		};

		led3 {
			label = "led3";
			gpios = <&gpm4 2 GPIO_ACTIVE_LOW>;
			default-state = "off";
		};

		led4 {
			label = "led4";
			gpios = <&gpm4 3 GPIO_ACTIVE_LOW>;
			default-state = "off";
			linux,default-trigger = "mmc0";
		};
	};

	fixed-rate-clocks {
		xxti {
			compatible = "samsung,clock-xxti";
			clock-frequency = <0>;
		};

		xusbxti {
			compatible = "samsung,clock-xusbxti";
			clock-frequency = <24000000>;
		};
	};
	interrupt_demo: interrupt_demo {
     compatible         = "tiny4412,interrupt_demo";
     tiny4412,int_gpio1 = <&gpx3 2 GPIO_ACTIVE_HIGH>;
     tiny4412,int_gpio2 = <&gpx3 3 GPIO_ACTIVE_HIGH>;
     tiny4412,int_gpio3 = <&gpx3 4 GPIO_ACTIVE_HIGH>;
     tiny4412,int_gpio4 = <&gpx3 5 GPIO_ACTIVE_HIGH>;
    };
};

&rtc {
	status = "okay";
};

&sdhci_2 {
	bus-width = <4>;
	pinctrl-0 = <&sd2_clk &sd2_cmd &sd2_cd &sd2_bus4>;
	pinctrl-names = "default";
	#status = "okay";	
	status = "disabled";
};

&serial_0 {
	status = "okay";
};

&serial_1 {
	status = "okay";
};

&serial_2 {
	status = "okay";
};

&serial_3 {
	status = "okay";
};

三、设备树驱动

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

typedef struct 
{
    int gpio;
    int irq;
    char name[20];
}int_demo_data_t;

static irqreturn_t int_demo_isr(int irq, void *dev_id)
{
    int_demo_data_t *data = dev_id;

    printk("%s enter, %s: gpio:%d, irq: %d\n", __func__, data->name, data->gpio, data->irq);

    return IRQ_HANDLED;
}

static int int_demo_probe(struct platform_device *pdev) {
    struct device *dev = &pdev->dev;
    int irq_gpio = -1;
    int irq = -1;
    int ret = 0;
    int i = 0;
    int_demo_data_t *data = NULL;

    printk("%s enter.\n", __func__);

    if (!dev->of_node) {
        dev_err(dev, "no platform data.\n");
        goto err1;
    }

    data = devm_kmalloc(dev, sizeof(*data)*4, GFP_KERNEL);
    if (!data) {
        dev_err(dev, "no memory.\n");
        goto err0;
    }

#if 1
    for (i = 3; i >= 0; i--) {
        sprintf(data[i].name, "tiny4412,int_gpio%d", i+1);
#else
    for (i = 0; i < 4; i++) {
#endif
        irq_gpio = of_get_named_gpio(dev->of_node, data[i].name, 0);//通过名字获取gpio
        if (irq_gpio < 0) {
            dev_err(dev, "Looking up %s property in node %s failed %d\n",
                data[i].name, dev->of_node->full_name, irq_gpio);
            goto err1;
        }

        data[i].gpio = irq_gpio;

        irq = gpio_to_irq(irq_gpio);    //将gpio转换成对应的中断号
        if (irq < 0) {
            dev_err(dev,
                "Unable to get irq number for GPIO %d, error %d\n",
                irq_gpio, irq);
            goto err1;
        }

        data[i].irq = irq;

        printk("%s: gpio: %d ---> irq (%d)\n", __func__, irq_gpio, irq);
    //注册中断
        ret = devm_request_any_context_irq(dev, irq, int_demo_isr, IRQF_TRIGGER_FALLING, data[i].name, data+i);
        if (ret < 0) {
            dev_err(dev, "Unable to claim irq %d; error %d\n",
                irq, ret);
            goto err1;
        }
    }

    return 0;

err1:
    devm_kfree(dev, data);
err0:
    return -EINVAL;
}

static int int_demo_remove(struct platform_device *pdev) {

    printk("%s enter.\n", __func__);

    return 0;
}

static const struct of_device_id int_demo_dt_ids[] = {
    { .compatible = "tiny4412,interrupt_demo", },
    {},
};

MODULE_DEVICE_TABLE(of, int_demo_dt_ids);

static struct platform_driver int_demo_driver = {
    .driver        = {
        .name      = "interrupt_demo",
        .of_match_table    = of_match_ptr(int_demo_dt_ids),
    },
    .probe         = int_demo_probe,
    .remove        = int_demo_remove,
};

static int __init int_demo_init(void)
{
    int ret;

    ret = platform_driver_register(&int_demo_driver);
    if (ret)
        printk(KERN_ERR "int demo: probe failed: %d\n", ret);

    return ret;
}
module_init(int_demo_init);

static void __exit int_demo_exit(void)
{
    platform_driver_unregister(&int_demo_driver);
}
module_exit(int_demo_exit);

MODULE_LICENSE("GPL");

编译驱动

KERN_DIR = /work/system/linux-3.4.2

all:
	make -C $(KERN_DIR) M=`pwd` modules 

clean:
	make -C $(KERN_DIR) M=`pwd` modules clean
	rm -rf modules.order

obj-m	+= mykey.o

采用了platform平台设备驱动的方式

platform_driver_register(&int_demo_driver);-->

.of_match_table    = of_match_ptr(int_demo_dt_ids),-->

.probe         = int_demo_probe,-->

of_get_named_gpio(dev->of_node, data[i].name, 0):将dev->of_node节点上的data[i].name的值取下。-->

irq = gpio_to_irq(irq_gpio);    //将gpio转换成对应的中断号-->

ret = devm_request_any_context_irq(dev, irq, int_demo_isr, IRQF_TRIGGER_FALLING, data[i].name, data+i);

//注册中断-->

中断发生-->

执行中断处理函数int_demo_isr-->

等待中断发生。

四、下载测试

#u-boot：

setenv bootargs  'root=/dev/nfs  rw  nfsroot=192.168.1.123:/work/nfs/rootfs_for_tiny4412/rootfs ethmac=1C:6F:65:34:51:7E  ip=192.168.1.125:192.168.1.123:192.168.1.1:255.255.255.0::eth0:off console=ttySAC0,115200  init=/linuxrc'

#u-boot：save

#u-boot：dnw 0x40600000

dnw arch/arm/boot/uImage

#u-boot：dnw 0x42000000

dnw  arch/arm/boot/dts/exynos4412-tiny4412.dtb

bootm 0x40600000 - 0x42000000