ARMLinux驱动Watch Dog Timer(看门狗)驱动分析

内核版本：2.6.28

主机平台：Ubuntu 11,04

内核版本：2.6.39

原创作品，转载请标明出处http://blog.csdn.net/yming0221/article/details/6595265

1、看门狗驱动的原理

下图是看门狗驱动的原理图

可以看出，PCLK是系统时钟，经过8位的预分频，然后再被分频（16、32、64、128）然后产生计数脉冲，进行计数，当计数器WTCNT加到0或减到0，然后产生中断，或引起系统复位。所以要隔一段时间，重置WTCNT的值，防止WTCNT减到0，称之“喂狗”。

2、驱动分析

下面是自己的驱动分析，如有理解错误，请指正

注，为了尽量是驱动容易理解，这个驱动暂时将有关电源管理的功能删除了，等理解透彻再完善

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 

#include 

#undef S3C_VA_WATCHDOG
#define S3C_VA_WATCHDOG (0)

#include 

#define PFX "s3c2410-wdt: "

#define CONFIG_S3C2410_WATCHDOG_ATBOOT		(0)
#define CONFIG_S3C2410_WATCHDOG_DEFAULT_TIME	(15)

static int nowayout	= WATCHDOG_NOWAYOUT;
static int tmr_margin	= CONFIG_S3C2410_WATCHDOG_DEFAULT_TIME;
static int tmr_atboot	= CONFIG_S3C2410_WATCHDOG_ATBOOT;
static int soft_noboot = 1; //设置默认为执行中断
static int debug;
static int count;//用于计数，控制LED灯的亮灭

module_param(tmr_margin,  int, 0);
module_param(tmr_atboot,  int, 0);
module_param(nowayout,    int, 0);
module_param(soft_noboot, int, 0);
module_param(debug,	  int, 0);

MODULE_PARM_DESC(tmr_margin, "Watchdog tmr_margin in seconds. default="
		__MODULE_STRING(CONFIG_S3C2410_WATCHDOG_DEFAULT_TIME) ")");
MODULE_PARM_DESC(tmr_atboot,
		"Watchdog is started at boot time if set to 1, default="
			__MODULE_STRING(CONFIG_S3C2410_WATCHDOG_ATBOOT));
MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default="
			__MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
MODULE_PARM_DESC(soft_noboot, "Watchdog action, set to 1 to ignore reboots, 0 to \
											reboot (default depends on ONLY_TESTING)");
MODULE_PARM_DESC(debug, "Watchdog debug, set to >1 for debug, (default 0)");


typedef enum close_state 
{
	CLOSE_STATE_NOT,
	CLOSE_STATE_ALLOW = 0x4021
} close_state_t;

static unsigned long open_lock;
static struct device    *wdt_dev;	/* platform device attached to */
static struct resource	*wdt_mem;//用来保存IO端口占用的内存资源
static struct resource	*wdt_irq;//保存wdt中断号
static struct clk	*wdt_clock;//保存从平台获取的watchdog时钟
static void __iomem	*wdt_base;//经过ioremap后的内存基地址
static unsigned int	 wdt_count;//保存向WTCNT写的计数值
static close_state_t	 allow_close;
static DEFINE_SPINLOCK(wdt_lock);//定义一个自旋锁，用于资源的互斥访问

/* watchdog control routines */

#define DBG(msg...) do { \
	if (debug) \
		printk(KERN_INFO msg); \
	} while (0)

/* functions */

//喂狗函数，实际上是将wdt_count写入WTCNT寄存器
static void s3c2410wdt_keepalive(void)
{
	spin_lock(&wdt_lock);//给资源上锁
	writel(wdt_count, wdt_base + S3C2410_WTCNT);//写WTCNT寄存器
	spin_unlock(&wdt_lock);//解锁资源,下同
}

static void __s3c2410wdt_stop(void)
{
	unsigned long wtcon;

	wtcon = readl(wdt_base + S3C2410_WTCON);
	wtcon &= ~(S3C2410_WTCON_ENABLE | S3C2410_WTCON_RSTEN);
	writel(wtcon, wdt_base + S3C2410_WTCON);//设备看门狗使能无效、复位功能无效
}
//停止watchdog计时
static void s3c2410wdt_stop(void)
{
	spin_lock(&wdt_lock);
	__s3c2410wdt_stop();
	spin_unlock(&wdt_lock);
}

//启动watchdog计时
static void s3c2410wdt_start(void)
{
	unsigned long wtcon;

	spin_lock(&wdt_lock);

	__s3c2410wdt_stop();

	wtcon = readl(wdt_base + S3C2410_WTCON);
	wtcon |= S3C2410_WTCON_ENABLE | S3C2410_WTCON_DIV128;//看门狗定时器使能、时钟除数因子128

	if (soft_noboot) //使用参数soft_noboot来选择看门狗到时是重启还是执行中断函数
	{
		wtcon |= S3C2410_WTCON_INTEN;//中断使能
		wtcon &= ~S3C2410_WTCON_RSTEN;//复位功能无效
	} 
	else 
	{
		wtcon &= ~S3C2410_WTCON_INTEN;//中断不使能
		wtcon |= S3C2410_WTCON_RSTEN;//复位功能有效
	}

	writel(wdt_count, wdt_base + S3C2410_WTDAT);//将wdt_count写入WTDAT
	writel(wdt_count, wdt_base + S3C2410_WTCNT);//将wdt_count写入WTCNT
	writel(wtcon, wdt_base + S3C2410_WTCON);//设置WTCON
	spin_unlock(&wdt_lock);
}

//设置WatchDog周期timeout
static int s3c2410wdt_set_heartbeat(int timeout)
{
	unsigned int freq = clk_get_rate(wdt_clock);
	unsigned int count;
	unsigned int divisor = 1;
	unsigned long wtcon;

	if (timeout < 1)
		return -EINVAL;

	freq /= 128;
	count = timeout * freq;

	/* if the count is bigger than the watchdog register,
	   then work out what we need to do (and if) we can
	   actually make this value
	*/
//如果计时的时间过大，则适当加大预分频值
	if (count >= 0x10000) 
	{
		for (divisor = 1; divisor <= 0x100; divisor++) 
		{
			if ((count / divisor) < 0x10000)
				break;
		}
//若预分频最大仍不能满足计时周期，则报错
		if ((count / divisor) >= 0x10000) 
		{
			dev_err(wdt_dev, "timeout %d too big\n", timeout);
			return -EINVAL;
		}
	}

	tmr_margin = timeout;

	count /= divisor;
	wdt_count = count;

	/* update the pre-scaler */
	wtcon = readl(wdt_base + S3C2410_WTCON);
	wtcon &= ~S3C2410_WTCON_PRESCALE_MASK;
	wtcon |= S3C2410_WTCON_PRESCALE(divisor-1);

	writel(count, wdt_base + S3C2410_WTDAT);//是指WTDAT寄存器
	writel(wtcon, wdt_base + S3C2410_WTCON);//设置预分频值

	return 0;
}

/*
 *	/dev/watchdog handling
 */

static int s3c2410wdt_open(struct inode *inode, struct file *file)
{
	if (test_and_set_bit(0, &open_lock))//测试并设置open_lock第0位为1
		return -EBUSY;
	if (nowayout)
		__module_get(THIS_MODULE);
		
	allow_close = CLOSE_STATE_NOT;

	/* start the timer */
	s3c2410wdt_start();//启动watchdog
	return nonseekable_open(inode, file);
}

static int s3c2410wdt_release(struct inode *inode, struct file *file)
{
	/*
	 *	Shut off the timer.
	 * 	Lock it in if it's a module and we set nowayout
	 */

	if (allow_close == CLOSE_STATE_ALLOW)
		s3c2410wdt_stop();
	else 
	{
		dev_err(wdt_dev, "Unexpected close, not stopping watchdog\n");
		s3c2410wdt_keepalive();
	}
	allow_close = CLOSE_STATE_NOT;
	clear_bit(0, &open_lock);//清楚open_lock第0位
	return 0;
}

static ssize_t s3c2410wdt_write(struct file *file, const char __user *data,
				size_t len, loff_t *ppos)
{
	/*
	 *	Refresh the timer.
	 */
	if (len) 
	{
		if (!nowayout) 
		{
			size_t i;
			/* In case it was set long ago */
			allow_close = CLOSE_STATE_NOT;

			for (i = 0; i != len; i++) 
			{
				char c;
				if (get_user(c, data + i))//从用户空间copy数据
					return -EFAULT;
				if (c == 'V')//当输入V时，关闭watchdog
					allow_close = CLOSE_STATE_ALLOW;
			}
		}
		//注意：这里要手动喂狗一次?!
		s3c2410wdt_keepalive();//由于将allow_close设置成CLOSE_STATE_ALLOW后，当release时无法再次喂狗
	}
	return len;
}

#define OPTIONS WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE

static const struct watchdog_info s3c2410_wdt_ident = 
{
	.options          =     OPTIONS,
	.firmware_version =	0,
	.identity         =	"S3C2410 Watchdog",
};

//IO控制接口函数
static long s3c2410wdt_ioctl(struct file *file,	unsigned int cmd,
							unsigned long arg)
{
	void __user *argp = (void __user *)arg;
	int __user *p = argp;
	int new_margin;

	switch (cmd) {
	case WDIOC_GETSUPPORT:
		return copy_to_user(argp, &s3c2410_wdt_ident,
			sizeof(s3c2410_wdt_ident)) ? -EFAULT : 0;
	case WDIOC_GETSTATUS:
	case WDIOC_GETBOOTSTATUS:
		return put_user(0, p);
	case WDIOC_KEEPALIVE:
		s3c2410wdt_keepalive();
		return 0;
	case WDIOC_SETTIMEOUT:
		if (get_user(new_margin, p))
			return -EFAULT;
		if (s3c2410wdt_set_heartbeat(new_margin))
			return -EINVAL;
		s3c2410wdt_keepalive();
		return put_user(tmr_margin, p);
	case WDIOC_GETTIMEOUT:
		return put_user(tmr_margin, p);
	default:
		return -ENOTTY;
	}
}

/* kernel interface */

//文件操作结构体
static const struct file_operations s3c2410wdt_fops = 
{
	.owner		= THIS_MODULE,
	.llseek		= no_llseek,//屏蔽seek操作
	.write		= s3c2410wdt_write,//写方法
	.unlocked_ioctl	= s3c2410wdt_ioctl,//控制方法
	.open		= s3c2410wdt_open,//代开设备方法
	.release	= s3c2410wdt_release,//关闭设备方法
};

static struct miscdevice s3c2410wdt_miscdev = 
{
	.minor		= WATCHDOG_MINOR,
	.name		= "watchdog",
	.fops		= &s3c2410wdt_fops,
};

/* interrupt handler code */

static irqreturn_t s3c2410wdt_irq(int irqno, void *param)
{
	//dev_info(wdt_dev, "watchdog timer expired (irq)\n");
	s3c2410_gpio_setpin(S3C2410_GPB10,(count++)%2);
	s3c2410wdt_keepalive();
	return IRQ_HANDLED;
}
/* device interface */

//注册设备时执行
static int s3c2410wdt_probe(struct platform_device *pdev)
{
	struct resource *res;
	struct device *dev;
	unsigned int wtcon;
	int started = 0;
	int ret;
	int size;

	dev = &pdev->dev;
	wdt_dev = &pdev->dev;

	/* get the memory region for the watchdog timer */
//获取IO端口资源，这里 IORESOURCE_MEM和平台设备中资源的定义一致
	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	if (res == NULL) {
		dev_err(dev, "no memory resource specified\n");
		return -ENOENT;
	}

	size = (res->end - res->start) + 1;
//申请内存空间
	wdt_mem = request_mem_region(res->start, size, pdev->name);
	if (wdt_mem == NULL) {
		dev_err(dev, "failed to get memory region\n");
		ret = -ENOENT;
		goto err_req;
	}
//地址映射，wdt_base为基地址
	wdt_base = ioremap(res->start, size);
	if (wdt_base == NULL) {
		dev_err(dev, "failed to ioremap() region\n");
		ret = -EINVAL;
		goto err_req;
	}

	DBG("probe: mapped wdt_base=%p\n", wdt_base);
//从平台设备中获取中断号
	wdt_irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
	if (wdt_irq == NULL) {
		dev_err(dev, "no irq resource specified\n");
		ret = -ENOENT;
		goto err_map;
	}
//注册中断，中断处理函数s3c2410wdt_irq()
	ret = request_irq(wdt_irq->start, s3c2410wdt_irq, 0, pdev->name, pdev);
	if (ret != 0) {
		dev_err(dev, "failed to install irq (%d)\n", ret);
		goto err_map;
	}
//获取系统时钟
	wdt_clock = clk_get(&pdev->dev, "watchdog");
	if (IS_ERR(wdt_clock)) {
		dev_err(dev, "failed to find watchdog clock source\n");
		ret = PTR_ERR(wdt_clock);
		goto err_irq;
	}
//使能时钟
	clk_enable(wdt_clock);

	/* see if we can actually set the requested timer margin, and if
	 * not, try the default value */

	if (s3c2410wdt_set_heartbeat(tmr_margin)) 
	{//这里第一次设置计时周期为tmr_margin，如果设置不成功，则重新设置为默认值
		started = s3c2410wdt_set_heartbeat(
					CONFIG_S3C2410_WATCHDOG_DEFAULT_TIME);

		if (started == 0)
			dev_info(dev,
			   "tmr_margin value out of range, default %d used\n",
			       CONFIG_S3C2410_WATCHDOG_DEFAULT_TIME);
		else
			dev_info(dev, "default timer value is out of range, cannot start\n");
	}
//注册设备
	ret = misc_register(&s3c2410wdt_miscdev);
	if (ret) 
	{
		dev_err(dev, "cannot register miscdev on minor=%d (%d)\n",
			WATCHDOG_MINOR, ret);
		goto err_clk;
	}

	if (tmr_atboot && started == 0) 
	{
		dev_info(dev, "starting watchdog timer\n");
		s3c2410wdt_start();//启动看门狗
	} 
	else if (!tmr_atboot) 
	{
		/* if we're not enabling the watchdog, then ensure it is
		 * disabled if it has been left running from the bootloader
		 * or other source */
		s3c2410wdt_stop();
	}

	/* print out a statement of readiness */

	wtcon = readl(wdt_base + S3C2410_WTCON);

	dev_info(dev, "watchdog %sactive, reset %sabled, irq %sabled\n",
		 (wtcon & S3C2410_WTCON_ENABLE) ?  "" : "in",
		 (wtcon & S3C2410_WTCON_RSTEN) ? "" : "dis",
		 (wtcon & S3C2410_WTCON_INTEN) ? "" : "en");
//设置GPB10端口为输出端口，用于点亮LED10
	s3c2410_gpio_cfgpin(S3C2410_GPB10,S3C2410_GPB10_OUTP);
	return 0;

//出错跳转表，异常处理

 err_clk:
	clk_disable(wdt_clock);
	clk_put(wdt_clock);

 err_irq:
	free_irq(wdt_irq->start, pdev);

 err_map:
	iounmap(wdt_base);

 err_req:
	release_resource(wdt_mem);
	kfree(wdt_mem);

	return ret;
}

//设备移除函数，释放资源和映射
static int s3c2410wdt_remove(struct platform_device *dev)
{
	release_resource(wdt_mem);
	kfree(wdt_mem);
	wdt_mem = NULL;

	free_irq(wdt_irq->start, dev);
	wdt_irq = NULL;

	clk_disable(wdt_clock);
	clk_put(wdt_clock);
	wdt_clock = NULL;

	iounmap(wdt_base);
	misc_deregister(&s3c2410wdt_miscdev);
	return 0;
}

//关闭看门狗
static void s3c2410wdt_shutdown(struct platform_device *dev)
{
	s3c2410wdt_stop();
}

//定义平台设备驱动
static struct platform_driver s3c2410wdt_driver = {
	.probe		= s3c2410wdt_probe,
	.remove		= s3c2410wdt_remove,
	.shutdown	= s3c2410wdt_shutdown,
	.driver		= {
		.owner	= THIS_MODULE,
		.name	= "s3c2410-wdt",//该名称参照内核源码中该资源的名称，两者必须一致
	},
};


static char banner[] __initdata =
	KERN_INFO "S3C2410 Watchdog Timer, (c) 2004 Simtec Electronics\n";

//驱动安装时执行
static int __init watchdog_init(void)
{
	printk(banner);
	return platform_driver_register(&s3c2410wdt_driver);//注册设备
}

//驱动移除是执行
static void __exit watchdog_exit(void)
{
	platform_driver_unregister(&s3c2410wdt_driver);//移除设备
}

module_init(watchdog_init);
module_exit(watchdog_exit);

MODULE_AUTHOR("Yan Ming");
MODULE_DESCRIPTION("S3C2410 Watchdog Device Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);