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.\n", 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\n"); 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\n"); 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。
