驱动程序实例（二）：LED设备驱动程序（ platform + /sys接口）

结合之前对Linux内核的platform总线 ，以及对Linux内核的LED设备的驱动框架的分析，本文将编写基于platform总线与/sys接口的LED设备的实例代码并对其进行分析。

platform总线分析，详见Linux platform驱动模型。

字符设备的cdev接口分析，详见Linux字符设备驱动框架（一）：Linux内核的LED设备驱动框架。

硬件接口：

　　CPU：s5pv210；

　　LED的GPIO：GPIO_J0_3 ~ GPIO_J0_5；

　　LED的工作方式：低电平亮，高电平灭。

使用Linux内核的LED驱动框架之前，需确保Linux内核支持LED驱动框架。进入Linux内核的配置界面menuconfig进行设置，具体配置如下：

　　Device Drivers  --->

　　　　[*] LED Support  --->    

本文将以两种形式编写LED驱动代码：

（1）将led_device和led_driver分别写成两个单独的文件模块；（这种做法适合学习使用）

（2）将led_device集成至Linux内核的/arch/arm/mach-s5pv210/mach-x210.c中，再将led_driver编写为独立模块。（这种做法更接近于实战的驱动程序，更好的使用设备树）

1.第一种写法

1.1 led_device.c

本文将设备信息写成一个模块的形式，需要时加载该模块即可。

#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/ioport.h>
#include <linux/platform_device.h>

//定义并初始化LED设备的相关资源
static struct resource led_resource = 
{
    .start = 0xE0200240,
    .end = 0xE0200240 + 8 - 1,
    .flags = IORESOURCE_MEM,
};

//定义并初始化LED设备信息
static struct platform_device led_dev = 
{
    .name = "led",             //设备名称
    .id = -1,                  //设备数量，-1表示只有一个设备
    .num_resources = 1,        //资源数量
    .resource = &led_resource, //资源指针
    .dev = 
    {
        .release = led_release,
    },
};

//注册LED设备
static int __init led_device_init(void)
{
    return platform_device_register(&led_dev);
}

//注销LED设备
static void __exit led_device_exit(void)
{
    platform_device_unregister(&led_dev);
}

module_init(led_device_init);
module_exit(led_device_exit);

MODULE_AUTHOR("Lin");
MODULE_DESCRIPTION("led device for x210");
MODULE_LICENSE("GPL");

1.2 led_driver.c

led_driver_init()：模块加载函数
　　platform_driver_register()将驱动对象模块注册到平台总线
　　led_probe()探测函数，提取相应的信息
　　　　platform_get_resource()获取设备资源
　　　　request_mem_region()、ioremap()虚拟内存映射
　　　　readl()、write()初始化硬件设备
　　　　kzalloc()申请led_classdev内存
　　　　led_classdev_register()注册LED设备

#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/ioport.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <asm/io.h>
#include <linux/leds.h>

//定义GPIO_J0寄存器变量
typedef struct GPJ0REG
{
    volatile unsigned int gpj0con;
    volatile unsigned int gpj0dat;
}gpj0_reg_t;

static gpj0_reg_t *pGPIOREG = NULL;
static struct led_classdev *led_cdev = NULL;

//LED设备实际的硬件操作函数
void led_brightness_set(struct led_classdev *led_cdev, enum led_brightness brightness)
{
    int reg_value = 0;
    
    //向LED设备属性文件brightness写入0，LED设备灭
    if (brightness == LED_OFF)
    {
        reg_value = readl(&(pGPIOREG->gpj0dat)); 
        reg_value |= (1 << 3) | (1 << 4) | (1 << 5);
        writel(reg_value, &(pGPIOREG->gpj0dat));
    }
    //否则，LED设备亮
    else
    {
        reg_value = readl(&(pGPIOREG->gpj0dat)); 
        reg_value &= ~((1 << 3) | (1 << 4) | (1 << 5));
        writel(reg_value, &(pGPIOREG->gpj0dat));
    }    
}

static int led_probe(struct platform_device *pdev)
{
    struct resource *res_led = NULL;
    int ret = -1;
    int reg_value = 0;
    
    /********************************申请资源*********************************/
    //获取资源
    res_led = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (!res_led) 
    {
        return -ENOMEM;
    }
    
    //动态内存映射
    if (!request_mem_region(res_led->start, resource_size(res_led), "GPIOJ0"))
    {
        return -EBUSY;
    }
    
    pGPIOREG = ioremap(res_led->start, resource_size(res_led));
    if (pGPIOREG ==  NULL) 
    {
        ret = -ENOENT;
        goto ERR_STEP;
    }
    
    /********************************设备初始化********************************/
    //初始化资源,设置GPIO为输出模式
    reg_value = readl(&(pGPIOREG->gpj0dat)); 
    reg_value |= (1 << (3*4)) | (1 << (4*4)) | (1 << (5*4));
    writel(reg_value, &(pGPIOREG->gpj0dat));
    
    /********************************创建接口**********************************/
    //申请led_classdev内存
    led_cdev = kzalloc(sizeof(struct led_classdev), GFP_KERNEL);
    if (led_cdev == NULL)
    {
        ret = -ENOMEM;
        goto ERR_STEP1;
    }
    
    led_cdev->name = pdev->name;
    led_cdev->brightness_set = led_brightness_set;
    
    //注册LED设备
    ret = led_classdev_register(NULL, led_cdev);
    if (ret) 
    {
        goto ERR_STEP2;
    }
    
    return 0;
    
    /******************************倒映式错误处理********************************/
ERR_STEP2:
    kfree(led_cdev);
    
ERR_STEP1:
    iounmap(pGPIOREG);    
    
ERR_STEP:
    release_mem_region(res_led->start, resource_size(res_led));
            
    return ret;
        
}
    
static int led_remove(struct platform_device *pdev)
{
    led_classdev_unregister(led_cdev); //注销LED设备
    iounmap(pGPIOREG);                   //释放内存
    kfree(led_cdev);                   //释放内存
    
    return 0;
}

//定义并初始化LED驱动信息
static struct platform_driver led_drv = 
{
    .driver = 
    {
        .name  = "led",
        .owner = THIS_MODULE,
    },
    .probe = led_probe,
    .remove = led_remove,
};

static int __init led_driver_init(void)
{
    return platform_driver_register(&led_drv);
}

static void __exit led_driver_exit(void)
{
    platform_driver_unregister(&led_drv);
}

module_init(led_driver_init);
module_exit(led_driver_exit);

MODULE_AUTHOR("Lin");
MODULE_DESCRIPTION("led driver for x210");
MODULE_LICENSE("GPL");

2.第二种写法

2.1 device

在/kernel/arch/arm/mach-s5pv210/include/mach目录下，建立一个leds_gpio.h文件，并填充如下内容。

#ifndef __ASM_ARCH_LEDSGPIO_H
#define __ASM_ARCH_LEDSGPIO_H "leds-gpio.h"

#define S3C24XX_LEDF_ACTLOW    (1<<0)        /* LED is on when GPIO low */
#define S3C24XX_LEDF_TRISTATE    (1<<1)      /* tristate to turn off */

//定义一个LED设备的数据结构
struct s3c24xx_led_platdata 
{
    unsigned int     gpio;
    unsigned int     flags;
    char            *name;
    char            *def_trigger;
};
#endif

在/kernel/arch/arm/mach-s5pv210/mach-x210.c下，添加如下内容，并添加对leds_gpio.h的包含。

/* LEDS */

static struct s5pv210_led_platdata s5pv210_led1_pdata = {
    .name        = "xled1",
    .gpio        = S5PV210_GPJ0(3),
    .flags       = S5PV210_LEDF_ACTLOW | S5PV210_LEDF_TRISTATE,
    .def_trigger = "heartbeat",
};

static struct s5pv210_led_platdata s5pv210_led2_pdata = {
    .name        = "xled2",
    .gpio        = S5PV210_GPJ0(4),
    .flags       = S5PV210_LEDF_ACTLOW | S5PV210_LEDF_TRISTATE,
    .def_trigger = "heartbeat",
};

static struct s5pv210_led_platdata s5pv210_led3_pdata = {
    .name        = "xled3",
    .gpio        = S5PV210_GPJ0(5),
    .flags       = S5PV210_LEDF_ACTLOW | S5PV210_LEDF_TRISTATE,
    .def_trigger = "heartbeat",
};

static struct platform_device s5pv210_led1 = {
    .name      = "s5pv210_led",
    .id        = 1,
    .dev       = {
        .platform_data    = &s5pv210_led1_pdata,
    },
};

static struct platform_device s5pv210_led2 = {
    .name      = "s5pv210_led",
    .id        = 2,
    .dev       = {
        .platform_data    = &s5pv210_led2_pdata,
    },
};

static struct platform_device s5pv210_led3 = {
    .name      = "s5pv210_led",
    .id        = 3,
    .dev       = {
        .platform_data   = &s5pv210_led3_pdata,
    },
};

将LED设备信息集成至smdkc110_devices，内核初始化时smdkc110_devices中的设备将被注册进内核。

static struct platform_device *smdkc110_devices[] __initdata = 
{
    ......
    &s5pv210_led1,
    &s5pv210_led2,
    &s5pv210_led3,
}; 

2.2 driver

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/leds.h>
#include <linux/gpio.h>
#include <linux/slab.h>

#include <mach/hardware.h>
#include <mach/regs-gpio.h>
#include <mach/leds-gpio.h>

#define X210_LED_OFF    1            // X210中LED是正极接电源，负极节GPIO
#define X210_LED_ON     0            // 所以1是灭，0是亮

struct s5pv210_gpio_led 
{
    struct led_classdev          cdev;
    struct s5pv210_led_platdata  *pdata; 
};

static inline struct s5pv210_gpio_led *pdev_to_gpio(struct platform_device *dev)
{
    return platform_get_drvdata(dev);
}

static inline struct s5pv210_gpio_led *to_gpio(struct led_classdev *led_cdev)
{
    return container_of(led_cdev, struct s5pv210_gpio_led, cdev);
}

//LED设备硬件操作函数
static void s5pv210_led_set(struct led_classdev *led_cdev, enum led_brightness value)
{
    struct s5pv210_gpio_led *led = to_gpio(led_cdev);
    struct s5pv210_led_platdata *pd = led->pdata;

    if (value == LED_OFF)
    {
        gpio_set_value(pd->gpio, X210_LED_OFF);
    }
    else
    {
        gpio_set_value(pd->gpio, X210_LED_ON);
    }

}


static int s5pv210_led_remove(struct platform_device *dev)
{
    struct s5pv210_gpio_led *led = pdev_to_gpio(dev);

    led_classdev_unregister(&led->cdev);//注销LED设备
    kfree(led);                         //释放内存
    gpio_free(led->pdata->gpio);        //释放GPIO

    return 0;
}

static int s5pv210_led_probe(struct platform_device *dev)
{
    struct s5pv210_led_platdata *pdata = dev->dev.platform_data;
    struct s5pv210_gpio_led *led;
    int ret;
    
    /*****************************申请GPIO资源******************************/
    ret = gpio_request(pdata->gpio, pdata->name);
    if (ret) 
    {
        printk(KERN_ERR "gpio_request failed, ret = %d.
", ret);
        return -EIO;
    } 
    
    /************************申请，并初始化GPIO资源*************************/
    // 设置为输出模式，并且默认输出1让LED灯灭
    gpio_direction_output(pdata->gpio, 1);

    
    /********************************创建接口********************************/
    led = kzalloc(sizeof(struct s5pv210_gpio_led), GFP_KERNEL);
    if (led == NULL) {
        dev_err(&dev->dev, "No memory for device
");
        return -ENOMEM;
    }

    platform_set_drvdata(dev, led);//将led存入dev->p->driver_data

    led->cdev.brightness_set = s5pv210_led_set;
    led->cdev.name = pdata->name;
    led->pdata = pdata;

    //注册LED设备
    ret = led_classdev_register(&dev->dev, &led->cdev);
    if (ret < 0) {
        dev_err(&dev->dev, "led_classdev_register failed
");
        kfree(led);
        return ret;
    }

    return 0;
}

//定义并初始化驱动信息
static struct platform_driver s5pv210_led_driver = {
    .probe        = s5pv210_led_probe,
    .remove       = s5pv210_led_remove,
    .driver       = 
　　{
        .name     = "s5pv210_led",
        .owner    = THIS_MODULE,
    },
};

//注册驱动
static int __init s5pv210_led_init(void)
{
    return platform_driver_register(&s5pv210_led_driver);
}

//注销驱动
static void __exit s5pv210_led_exit(void)
{
    platform_driver_unregister(&s5pv210_led_driver);
}

module_init(s5pv210_led_init);
module_exit(s5pv210_led_exit);

MODULE_AUTHOR("Ben Dooks <ben@simtec.co.uk>");
MODULE_DESCRIPTION("S5PV210 LED driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:s5pv210_led");

3. 测试

装载上述两个模块（device、driver）之后，进入/sys/class/leds目录下，会发现多了一个led文件夹。进入led文件夹，会看到LED设备的属性文件。

（1）向属性文件brightness写入0，"  echo  0  >  brightness "，LED设备灭；

（2）向属性文件brightness写入1，"  echo  1  >  brightness "，LED设备亮；

（3）读取属性文件max_brightness，" cat  max_brightness "，获取LED设备的最大亮度值。