驱动学习回顾——platform总线驱动-结合LED实例分析
前一篇文章总结了Linux下的bus设备模型，实际上，我们在编程过程中，并不需要自己来创建总线，Linux已经为我们实现了诸如platform总线、USB总线、I2C总线等等。
而接下来要学习总结的platform总线有点“特别”，与USB、I2C、SPI等物理总线不同，它是一条虚拟总线。像USB设备、I2C设备都会有自己对应类型的总线进行挂载，从而与CPU通信。但是在嵌入式系统中，并不是所有的设备都能归属于这些常见的总线，所以Linux为了保证设备驱动的统一和完整，“虚拟”出了这么一条总线。
platform只是Linux总线模型下的一个子类。
下面以以前做过的在platform上实现的LED驱动程序来进行总结。
和之前一样先从__init 入手：
一、
static int __init s3c_led_init(void)
{
int ret = 0;
ret = platform_device_register(&s3c_led_device);
if(ret)
{
printk(KERN_ERR "%s:%d: Can't register platform device %d\n", __FUNCTION__,__LINE__, ret);
goto fail_reg_plat_dev;
}
dbg_print("Regist S3C LED Platform Device successfully.\n");
ret = platform_driver_register(&s3c_led_driver);
if(ret)
{
printk(KERN_ERR "%s:%d: Can't register platform driver %d\n", __FUNCTION__,__LINE__, ret);
goto fail_reg_plat_drv;
}
dbg_print("Regist S3C LED Platform Driver successfully.\n");
return 0;
fail_reg_plat_drv:
platform_driver_unregister(&s3c_led_driver);
fail_reg_plat_dev:
return ret;
}1、可以看到在这个s3c_led_init 函数中s3c_led_device 是通过platform_device_register 进行了设备的注册。
//drivers/base/platform.c
int platform_device_register(struct platform_device *pdev)
{
device_initialize(&pdev->dev);
return platform_device_add(pdev);
}
EXPORT_SYMBOL_GPL(platform_device_register);platform_device_register 进而调用platform_device_add
，在这个函数里会将父设备设置为 platform_bus(即：/sys/devices/platform)，然后设置将设备挂在platform 总线下(即：platform_bus_type)，接着对平台设备资源做处理，最后将平台设备添加入系统中(即：/sys/devices/platform/xxx)。
2、s3c_led_init 中接着进行驱动的注册platform_driver_register。同样看到这个函数：
//drivers/base/platform.c
/**
* platform_driver_register - register a driver for platform-level devices
* @drv: platform driver structure
*/
int platform_driver_register(struct platform_driver *drv)
{
drv->driver.bus = &platform_bus_type; //设备驱动挂在platform下
/*对 drv 中的函数指针进行填充*/
if (drv->probe)
drv->driver.probe = platform_drv_probe;
if (drv->remove)
drv->driver.remove = platform_drv_remove;
if (drv->shutdown)
drv->driver.shutdown = platform_drv_shutdown;
return driver_register(&drv->driver); //注册设备驱动
}
EXPORT_SYMBOL_GPL(platform_driver_register);二、
接下来进入s3c_led_device 看看：
static struct platform_device s3c_led_device = {
.name = "s3c_led",
.id = 1,
.dev =
{
.platform_data = &s3c_led_data,
.release = platform_led_release,
},
};里面的name id 是为后面的match 驱动和设备的匹配，platform_data 存放的是设个设备（led）的资源。继续进入s3c_led_data：
static struct s3c_led_platform_data s3c_led_data = {
.leds = s3c_leds,
.nleds = ARRAY_SIZE(s3c_leds),
};进入s3c_leds：
static struct s3c_led_info s3c_leds[] = {
[0] = {
.num = 1,
.gpio = S3C2410_GPB(5),
.active_level = LOWLEVEL,
.status = OFF,
.blink = ENABLE,
},
[1] = {
.num = 2,
.gpio = S3C2410_GPB(6),
.active_level = LOWLEVEL,
.status = OFF,
.blink = DISABLE,
},
[2] = {
.num = 3,
.gpio = S3C2410_GPB(8),
.active_level = LOWLEVEL,
.status = OFF,
.blink = DISABLE,
},
[3] = {
.num = 4,
.gpio = S3C2410_GPB(10),
.active_level = LOWLEVEL,
.status = OFF,
.blink = DISABLE,
},
};这是一个结构体类型的数组s3c_leds[] ，里面的成员就保存的是每一个设备的物理属性。
三、
再来看驱动是怎么运作的，s3c_led_driver：
static struct platform_driver s3c_led_driver = {
.probe = s3c_led_probe,
.remove = s3c_led_remove,
.driver = {
.name = "s3c_led",
.owner = THIS_MODULE,
},
};看到了熟悉的身影: probe ，前一篇博文讲到，probe 在驱动匹配完成后执行，用以驱动的初始化。remove 也提到了，是用作驱动和设备分离、释放的。只要驱动或设备有一方离开了总线，就会执行这个函数。
probe：（分成几个来看）
static int s3c_led_probe(struct platform_device *dev)
{
struct s3c_led_platform_data *pdata = dev->dev.platform_data;
int result = 0;
int i;
dev_t devno;下面是LED的初始化，nleds 前面有，是一共4个led灯。全部熄灭作为初始状态。
/* Initialize the LED status */
for(i=0; inleds; i++)
{
s3c2410_gpio_cfgpin(pdata->leds[i].gpio, S3C2410_GPIO_OUTPUT);
if(ON == pdata->leds[i].status)
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, pdata->leds[i].active_level);
}
else
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, ~pdata->leds[i].active_level);
}
} 下面的代码部分就很熟悉了，跟普通字符设备的流程相似。1.分配主、次设备号（手动分配 or 自动分配）；2.cdev_init 创建字符设备结构体变量，并与led_fops (file operation)关联起来，cdev_add 将该设备添加进内核
/* Alloc the device for driver */
if (0 != dev_major)
{
devno = MKDEV(dev_major, dev_minor);
result = register_chrdev_region(devno, 1, DEV_NAME);
}
else
{
result = alloc_chrdev_region(&devno, dev_minor, 1, DEV_NAME);
dev_major = MAJOR(devno);
}
/* Alloc for device major failure */
if (result < 0)
{
printk("%s driver can't get major %d\n", DEV_NAME, dev_major);
return result;
}
/* Initialize led structure and register cdev*/
memset(&led_device, 0, sizeof(led_device));
led_device.data = dev->dev.platform_data;
cdev_init (&(led_device.cdev), &led_fops);
led_device.cdev.owner = THIS_MODULE;
result = cdev_add (&(led_device.cdev), devno , 1);
if (result)
{
printk (KERN_NOTICE "error %d add %s device", result, DEV_NAME);
goto ERROR;
} 下面这段代码是自动创建设备节点，省掉了手动mknode 的过程。
led_device.dev_class = class_create(THIS_MODULE, DEV_NAME);
if(IS_ERR(led_device.dev_class))
{
printk("%s driver create class failture\n",DEV_NAME);
result = -ENOMEM;
goto ERROR;
}
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,24)
device_create(led_device.dev_class, NULL, devno, NULL, DEV_NAME);
#else
device_create (led_device.dev_class, NULL, devno, DEV_NAME);
#endif下面一段是跟定时器有关，等下再看led_timer_handler 做了什么。
/* Initial the LED blink timer */
init_timer(&(led_device.blink_timer));
led_device.blink_timer.function = led_timer_handler;
led_device.blink_timer.data = (unsigned long)pdata;
led_device.blink_timer.expires = jiffies + TIMER_TIMEOUT;
add_timer(&(led_device.blink_timer)); 下面就是打印信息、出错处理了。
printk("S3C %s driver version %d.%d.%d initiliazed.\n", DEV_NAME, DRV_MAJOR_VER, DRV_MINOR_VER, DRV_REVER_VER);
return 0;
ERROR:
printk("S3C %s driver version %d.%d.%d install failure.\n", DEV_NAME, DRV_MAJOR_VER, DRV_MINOR_VER, DRV_REVER_VER);
cdev_del(&(led_device.cdev));
unregister_chrdev_region(devno, 1);
return result;
}下面是有关定时器的函数：
void led_timer_handler(unsigned long data)
{
int i;
struct s3c_led_platform_data *pdata = (struct s3c_led_platform_data *)data;
for(i=0; inleds; i++)
{
if(ON == pdata->leds[i].status)
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, pdata->leds[i].active_level);
}
else
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, ~pdata->leds[i].active_level);
}
if(ENABLE == pdata->leds[i].blink ) /* LED should blink */
{
/* Switch status between 0 and 1 to turn LED ON or off */
pdata->leds[i].status = pdata->leds[i].status ^ 0x01;
}
mod_timer(&(led_device.blink_timer), jiffies + TIMER_TIMEOUT);
}
} 这段代码作用就是：定时读取每一个LED的引脚状态到active_level 里，若设备有开启blink 则在每个循环内反转一次状态。
请留意这里有一个mod_timer ，mod_timer()会重新注册定时器到内核，而不管定时器函数是否被运行过。
注意！一个重要的知识点：jiffies。 关于jiffies考虑单独做一个总结，这个机制很有参考意义，比如可以借鉴到单片机的开发上。这里先留一个引子。
remove：
static int s3c_led_remove(struct platform_device *dev)
{
dev_t devno = MKDEV(dev_major, dev_minor);
del_timer(&(led_device.blink_timer));
cdev_del(&(led_device.cdev));
device_destroy(led_device.dev_class, devno);
class_destroy(led_device.dev_class);
unregister_chrdev_region(devno, 1);
printk("S3C %s driver removed\n", DEV_NAME);
return 0;
}这也是有一套流程的：回收主设备号；注销字符设备变量；这里新增了清除定时器和销毁dev_class 。
四、
注销平台设备：
static void s3c_led_exit(void)
{
dbg_print("%s():%d remove LED platform drvier\n", __FUNCTION__,__LINE__);
platform_driver_unregister(&s3c_led_driver);
dbg_print("%s():%d remove LED platform device\n", __FUNCTION__,__LINE__);
platform_device_unregister(&s3c_led_device);
}很简单，platform_driver_unregister 注销驱动，platform_device_unregister 注销设备。
整个led实例的过程以图示说明：（比较简陋，仅供参考。。）
关于platform在内核中是如何一步步添加到bus上的就不深究了。从网上摘录一个图：
最后给出完整代码：
#include "s3c_driver.h"
#define DRV_AUTHOR "Tangbin"
#define DRV_DESC "S3C24XX LED driver"
/* Driver version*/
#define DRV_MAJOR_VER 1
#define DRV_MINOR_VER 0
#define DRV_REVER_VER 0
#define DEV_NAME DEV_LED_NAME
//#define DEV_MAJOR DEV_LED_MAJOR
#ifndef DEV_MAJOR
#define DEV_MAJOR 0 /* dynamic major by default */
#endif
#define TIMER_TIMEOUT 40
static int debug = DISABLE;
static int dev_major = DEV_MAJOR;
static int dev_minor = 0;
/* ============================ Platform Device part ===============================*/
/* LED hardware informtation structure*/
struct s3c_led_info
{
unsigned char num; /* The LED number */
unsigned int gpio; /* Which GPIO the LED used */
unsigned char active_level; /* The GPIO pin level(HIGHLEVEL or LOWLEVEL) to turn on or off */
unsigned char status; /* Current LED status: OFF/ON */
unsigned char blink; /* Blink or not */
};
/* The LED platform device private data structure */
struct s3c_led_platform_data
{
struct s3c_led_info *leds;
int nleds;
};
/* LED hardware informtation data*/
static struct s3c_led_info s3c_leds[] = {
[0] = {
.num = 1,
.gpio = S3C2410_GPB(5),
.active_level = LOWLEVEL,
.status = OFF,
.blink = ENABLE,
},
[1] = {
.num = 2,
.gpio = S3C2410_GPB(6),
.active_level = LOWLEVEL,
.status = OFF,
.blink = DISABLE,
},
[2] = {
.num = 3,
.gpio = S3C2410_GPB(8),
.active_level = LOWLEVEL,
.status = OFF,
.blink = DISABLE,
},
[3] = {
.num = 4,
.gpio = S3C2410_GPB(10),
.active_level = LOWLEVEL,
.status = OFF,
.blink = DISABLE,
},
};
/* The LED platform device private data */
static struct s3c_led_platform_data s3c_led_data = {
.leds = s3c_leds,
.nleds = ARRAY_SIZE(s3c_leds),
};
struct led_device
{
struct s3c_led_platform_data *data;
struct cdev cdev;
struct class *dev_class;
struct timer_list blink_timer;
} led_device;
static void platform_led_release(struct device * dev)
{
int i;
struct s3c_led_platform_data *pdata = dev->platform_data;
dbg_print("%s():%d\n", __FUNCTION__,__LINE__);
/* Turn all LED off */
for(i=0; inleds; i++)
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, ~pdata->leds[i].active_level);
}
}
static struct platform_device s3c_led_device = {
.name = "s3c_led",
.id = 1,
.dev =
{
.platform_data = &s3c_led_data,
.release = platform_led_release,
},
};
/* ===================== led device driver part ===========================*/
void led_timer_handler(unsigned long data)
{
int i;
struct s3c_led_platform_data *pdata = (struct s3c_led_platform_data *)data;
for(i=0; inleds; i++)
{
if(ON == pdata->leds[i].status)
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, pdata->leds[i].active_level);
}
else
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, ~pdata->leds[i].active_level);
}
if(ENABLE == pdata->leds[i].blink ) /* LED should blink */
{
/* Switch status between 0 and 1 to turn LED ON or off */
pdata->leds[i].status = pdata->leds[i].status ^ 0x01;
}
mod_timer(&(led_device.blink_timer), jiffies + TIMER_TIMEOUT);
}
}
static int led_open(struct inode *inode, struct file *file)
{
struct led_device *pdev ;
struct s3c_led_platform_data *pdata;
pdev = container_of(inode->i_cdev,struct led_device, cdev);
pdata = pdev->data;
file->private_data = pdata;
return 0;
}
static int led_release(struct inode *inode, struct file *file)
{
return 0;
}
static void print_led_help(void)
{
printk("Follow is the ioctl() command for LED driver:\n");
printk("Enable Driver debug command: %u\n", SET_DRV_DEBUG);
printk("Get Driver verion command : %u\n", GET_DRV_VER);
printk("Turn LED on command : %u\n", LED_ON);
printk("Turn LED off command : %u\n", LED_OFF);
printk("Turn LED blink command : %u\n", LED_BLINK);
}
/* compatible with kernel version >=2.6.38*/
static long led_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct s3c_led_platform_data *pdata = file->private_data;
switch (cmd)
{
case SET_DRV_DEBUG:
dbg_print("%s driver debug now.\n", DISABLE == arg ? "Disable" : "Enable");
debug = (0==arg) ? DISABLE : ENABLE;
break;
case GET_DRV_VER:
print_version(DRV_VERSION);
return DRV_VERSION;
case LED_OFF:
if(pdata->nleds <= arg)
{
printk("LED%ld doesn't exist\n", arg);
return -ENOTTY;
}
pdata->leds[arg].status = OFF;
pdata->leds[arg].blink = DISABLE;
break;
case LED_ON:
if(pdata->nleds <= arg)
{
printk("LED%ld doesn't exist\n", arg);
return -ENOTTY;
}
pdata->leds[arg].status = ON;
pdata->leds[arg].blink = DISABLE;
break;
case LED_BLINK:
if(pdata->nleds <= arg)
{
printk("LED%ld doesn't exist\n", arg);
return -ENOTTY;
}
pdata->leds[arg].blink = ENABLE;
pdata->leds[arg].status = ON;
break;
default:
dbg_print("%s driver don't support ioctl command=%d\n", DEV_NAME, cmd);
print_led_help();
return -EINVAL;
}
return 0;
}
static struct file_operations led_fops = {
.owner = THIS_MODULE,
.open = led_open,
.release = led_release,
.unlocked_ioctl = led_ioctl, /* compatible with kernel version >=2.6.38*/
};
static int s3c_led_probe(struct platform_device *dev)
{
struct s3c_led_platform_data *pdata = dev->dev.platform_data;
int result = 0;
int i;
dev_t devno;
/* Initialize the LED status */
for(i=0; inleds; i++)
{
s3c2410_gpio_cfgpin(pdata->leds[i].gpio, S3C2410_GPIO_OUTPUT);
if(ON == pdata->leds[i].status)
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, pdata->leds[i].active_level);
}
else
{
s3c2410_gpio_setpin(pdata->leds[i].gpio, ~pdata->leds[i].active_level);
}
}
/* Alloc the device for driver */
if (0 != dev_major)
{
devno = MKDEV(dev_major, dev_minor);
result = register_chrdev_region(devno, 1, DEV_NAME);
}
else
{
result = alloc_chrdev_region(&devno, dev_minor, 1, DEV_NAME);
dev_major = MAJOR(devno);
}
/* Alloc for device major failure */
if (result < 0)
{
printk("%s driver can't get major %d\n", DEV_NAME, dev_major);
return result;
}
/* Initialize button structure and register cdev*/
memset(&led_device, 0, sizeof(led_device));
led_device.data = dev->dev.platform_data;
cdev_init (&(led_device.cdev), &led_fops);
led_device.cdev.owner = THIS_MODULE;
result = cdev_add (&(led_device.cdev), devno , 1);
if (result)
{
printk (KERN_NOTICE "error %d add %s device", result, DEV_NAME);
goto ERROR;
}
led_device.dev_class = class_create(THIS_MODULE, DEV_NAME);
if(IS_ERR(led_device.dev_class))
{
printk("%s driver create class failture\n",DEV_NAME);
result = -ENOMEM;
goto ERROR;
}
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,24)
device_create(led_device.dev_class, NULL, devno, NULL, DEV_NAME);
#else
device_create (led_device.dev_class, NULL, devno, DEV_NAME);
#endif
/* Initial the LED blink timer */
init_timer(&(led_device.blink_timer));
led_device.blink_timer.function = led_timer_handler;
led_device.blink_timer.data = (unsigned long)pdata;
led_device.blink_timer.expires = jiffies + TIMER_TIMEOUT;
add_timer(&(led_device.blink_timer));
printk("S3C %s driver version %d.%d.%d initiliazed.\n", DEV_NAME, DRV_MAJOR_VER, DRV_MINOR_VER, DRV_REVER_VER);
return 0;
ERROR:
printk("S3C %s driver version %d.%d.%d install failure.\n", DEV_NAME, DRV_MAJOR_VER, DRV_MINOR_VER, DRV_REVER_VER);
cdev_del(&(led_device.cdev));
unregister_chrdev_region(devno, 1);
return result;
}
static int s3c_led_remove(struct platform_device *dev)
{
dev_t devno = MKDEV(dev_major, dev_minor);
del_timer(&(led_device.blink_timer));
cdev_del(&(led_device.cdev));
device_destroy(led_device.dev_class, devno);
class_destroy(led_device.dev_class);
unregister_chrdev_region(devno, 1);
printk("S3C %s driver removed\n", DEV_NAME);
return 0;
}
static struct platform_driver s3c_led_driver = {
.probe = s3c_led_probe,
.remove = s3c_led_remove,
.driver = {
.name = "s3c_led",
.owner = THIS_MODULE,
},
};
static int __init s3c_led_init(void)
{
int ret = 0;
ret = platform_device_register(&s3c_led_device);
if(ret)
{
printk(KERN_ERR "%s:%d: Can't register platform device %d\n", __FUNCTION__,__LINE__, ret);
goto fail_reg_plat_dev;
}
dbg_print("Regist S3C LED Platform Device successfully.\n");
ret = platform_driver_register(&s3c_led_driver);
if(ret)
{
printk(KERN_ERR "%s:%d: Can't register platform driver %d\n", __FUNCTION__,__LINE__, ret);
goto fail_reg_plat_drv;
}
dbg_print("Regist S3C LED Platform Driver successfully.\n");
return 0;
fail_reg_plat_drv:
platform_driver_unregister(&s3c_led_driver);
fail_reg_plat_dev:
return ret;
}
static void s3c_led_exit(void)
{
dbg_print("%s():%d remove LED platform drvier\n", __FUNCTION__,__LINE__);
platform_driver_unregister(&s3c_led_driver);
dbg_print("%s():%d remove LED platform device\n", __FUNCTION__,__LINE__);
platform_device_unregister(&s3c_led_device);
}
module_init(s3c_led_init);
module_exit(s3c_led_exit);
module_param(debug, int, S_IRUGO);
module_param(dev_major, int, S_IRUGO);
module_param(dev_minor, int, S_IRUGO);
MODULE_AUTHOR(DRV_AUTHOR);
MODULE_DESCRIPTION(DRV_DESC);
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:S3C24XX_led"); 参考资料：
http://www.cnblogs.com/deng-tao/p/6026373.html
http://blog.csdn.net/qq_695538007/article/details/40456875
http://blog.csdn.net/u011164819/article/details/50186905
http://www.cnblogs.com/chenfulin5/p/5690661.html