S3C2440驱动篇—看门狗驱动分析

看门狗WatchDog驱动

      Linux-2.6.32.2内核自带S3C2440看门狗驱动，只需要配置一下就可以使用。驱动源代码位于drivers/watchdog/s3c2410_wdt.c，由于驱动使用了平台设备，有关平台设备学习参考上一篇文章。

驱动实现：

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/types.h>
#include <linux/timer.h>
#include <linux/miscdevice.h>
#include <linux/watchdog.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/interrupt.h>
#include <linux/clk.h>
#include <linux/uaccess.h>
#include <linux/io.h>

#include <mach/map.h>

#undef S3C_VA_WATCHDOG
#define S3C_VA_WATCHDOG (0)

#include <plat/regs-watchdog.h>

#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;
static int debug;

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);

static unsigned long open_lock;
static struct device    *wdt_dev;	/* platform device attached to */
static struct resource	*wdt_mem;
static struct resource	*wdt_irq;
static struct clk	*wdt_clock;
static void __iomem	*wdt_base;
static unsigned int	 wdt_count;
static char		 expect_close;
static DEFINE_SPINLOCK(wdt_lock);

/* watchdog control routines */

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

/* functions */

static void s3c2410wdt_keepalive(void) //喂狗
{
	spin_lock(&wdt_lock);
	writel(wdt_count, wdt_base + S3C2410_WTCNT);
	spin_unlock(&wdt_lock);
}

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);
}

static void s3c2410wdt_stop(void)   //停止看门狗
{
	spin_lock(&wdt_lock);
	__s3c2410wdt_stop();
	spin_unlock(&wdt_lock);
}

static void s3c2410wdt_start(void)  //启动看门狗
{
	unsigned long wtcon;

	spin_lock(&wdt_lock);

	__s3c2410wdt_stop();

	wtcon = readl(wdt_base + S3C2410_WTCON);
	wtcon |= S3C2410_WTCON_ENABLE | S3C2410_WTCON_DIV128;

	if (soft_noboot) {
		wtcon |= S3C2410_WTCON_INTEN;
		wtcon &= ~S3C2410_WTCON_RSTEN;
	} else {
		wtcon &= ~S3C2410_WTCON_INTEN;
		wtcon |= S3C2410_WTCON_RSTEN;
	}

	DBG("%s: wdt_count=0x%08x, wtcon=%08lx\n",
	    __func__, wdt_count, wtcon);

	writel(wdt_count, wdt_base + S3C2410_WTDAT);
	writel(wdt_count, wdt_base + S3C2410_WTCNT);
	writel(wtcon, wdt_base + S3C2410_WTCON);
	spin_unlock(&wdt_lock);
}

static int s3c2410wdt_set_heartbeat(int timeout)   //根据timeout时间设置看门狗定时器初始值
{
	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;

	DBG("%s: count=%d, timeout=%d, freq=%d\n",
	    __func__, 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
	*/

	if (count >= 0x10000) {
		for (divisor = 1; divisor <= 0x100; divisor++) {
			if ((count / divisor) < 0x10000)
				break;
		}

		if ((count / divisor) >= 0x10000) {
			dev_err(wdt_dev, "timeout %d too big\n", timeout);
			return -EINVAL;
		}
	}

	tmr_margin = timeout;

	DBG("%s: timeout=%d, divisor=%d, count=%d (%08x)\n",
	    __func__, timeout, divisor, count, count/divisor);

	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);
	writel(wtcon, wdt_base + S3C2410_WTCON);

	return 0;
}

/*
 *	/dev/watchdog handling
 */

static int s3c2410wdt_open(struct inode *inode, struct file *file)
{
	if (test_and_set_bit(0, &open_lock))
		return -EBUSY;

	if (nowayout)     /*nowayout是内涵配置选项，如果配置则看门狗不能被关闭*/
		__module_get(THIS_MODULE);/*如果内核配置了CONFIG_WATCHDOG_NOWAYOUT项，则使模块使用计数加1*/

	expect_close = 0;

	/* start the timer */
	s3c2410wdt_start();
	return nonseekable_open(inode, file);/*表示返回的这个设备文件是不可以被seek操作的，nonseekable_open定义在fs.h中*/
}

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 (expect_close == 42)
		s3c2410wdt_stop();
	else {
		dev_err(wdt_dev, "Unexpected close, not stopping watchdog\n");
		s3c2410wdt_keepalive();
	}
	expect_close = 0;
	clear_bit(0, &open_lock);
	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) { /*如果没有配置内核CONFIG_WATCHDOG_NOWAYOUT选项,WATCHDOG_NOWAYOUT宏位于include/linux/watchdog.h*/
			size_t i;

			/* In case it was set long ago */
			expect_close = 0;

			for (i = 0; i != len; i++) {
				char c;

				if (get_user(c, data + i))
					return -EFAULT;
				if (c == 'V')
					expect_close = 42;
			}
		}
/*上面的意思是想要看门狗定时器可以被关闭，则内核不要配置CONFIG_WATCHDOG_NOWAYOUT选项，对于下面这里还要“喂狗”一次，我刚开始觉得不需要，因为在看门狗定时器中断里面不断的在“喂狗”。后来想想，这里还必须要“喂狗”一次，因为当上面我们判断到写入的数据是"V"时，看门狗定时器的当前操作状态马上被设置为关闭，再当驱动去调用看门狗设备驱动的关闭接口函数时，看门狗定时器中断被禁止，无法再实现“喂狗”，所以这里要手动“喂狗”一次，否则定时器溢出系统被复位*/

		s3c2410wdt_keepalive();
	}
	return len;
}

#define OPTIONS (WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE)

/*用于支持看门狗IO控制中获取看门狗信息的命令WDIOC_GETSUPPORT，下面的宏和看门狗信息结构体定义在include/linux/watchdog.h中*/
static const struct watchdog_info s3c2410_wdt_ident = {
	.options          =     OPTIONS,
	.firmware_version =	0,
	.identity         =	"S3C2410 Watchdog",
};


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;

	/*以下对看门狗定时器IO控制的命令定义在watchdog.h中*/
	switch (cmd) {
	case WDIOC_GETSUPPORT:/*获取看门狗的支持信息，wdt_ident定义在上面*/
		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 */

static const struct file_operations s3c2410wdt_fops = {
	.owner		= THIS_MODULE,
	.llseek		= no_llseek,  /*定义为不可定位，即屏蔽seek操作，no_llseek定义在fs.h中*/
	.write		= s3c2410wdt_write,
	.unlocked_ioctl	= s3c2410wdt_ioctl,
	.open		= s3c2410wdt_open,
	.release	= s3c2410wdt_release,
};

static struct miscdevice s3c2410wdt_miscdev = {
	.minor		= WATCHDOG_MINOR,  //位于include/linux/miscdevic.h中
	.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");

	s3c2410wdt_keepalive();
	return IRQ_HANDLED;
}
/* device interface */

static int __devinit s3c2410wdt_probe(struct platform_device *pdev)
{
	struct resource *res;  /*定义一个资源，用来保存获取的watchdog的IO资源*/
	struct device *dev;
	unsigned int wtcon;
	int started = 0;
	int ret;
	int size;

	DBG("%s: probe=%p\n", __func__, pdev);

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

	/* get the memory region for the watchdog timer */

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	if (res == NULL) {
		/*dev_err定义在device.h中，在platform_device.h中已经引用，所以这里就不需再引用*/
		dev_err(dev, "no memory resource specified\n");
		return -ENOENT;
	}

	size = (res->end - res->start) + 1;
       /*申请watchdog的IO端口资源所占用的IO内存,request_mem_region定义在ioport.h中*/
	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;
	}

	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);

	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;
	}

	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;
	}
	/*定义在arch/arm/plat-s3c24xx/s3c2410-clock.c中*/
	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;
	}

	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)) {
		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");
	}

	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();
	} 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");

	return 0;

 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;
}

static int __devexit 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;
}

static void s3c2410wdt_shutdown(struct platform_device *dev)
{
	s3c2410wdt_stop();
}

#ifdef CONFIG_PM
/*对Watchdog平台设备驱动电源管理的支持。CONFIG_PM这个宏定义在内核中，当配置内核时选上电源管理，则Watchdog平台驱动的设备挂起和恢复功能均有效*/

static unsigned long wtcon_save;
static unsigned long wtdat_save;

static int s3c2410wdt_suspend(struct platform_device *dev, pm_message_t state)
{
	/* Save watchdog state, and turn it off. */
	wtcon_save = readl(wdt_base + S3C2410_WTCON);
	wtdat_save = readl(wdt_base + S3C2410_WTDAT);

	/* Note that WTCNT doesn't need to be saved. */
	s3c2410wdt_stop();

	return 0;
}

static int s3c2410wdt_resume(struct platform_device *dev)
{
	/* Restore watchdog state. */

	writel(wtdat_save, wdt_base + S3C2410_WTDAT);
	writel(wtdat_save, wdt_base + S3C2410_WTCNT); /* Reset count */
	writel(wtcon_save, wdt_base + S3C2410_WTCON);

	printk(KERN_INFO PFX "watchdog %sabled\n",
	       (wtcon_save & S3C2410_WTCON_ENABLE) ? "en" : "dis");

	return 0;
}

#else
#define s3c2410wdt_suspend NULL
#define s3c2410wdt_resume  NULL
#endif /* CONFIG_PM */

/*注意：这是使用了一个__devexit_p，还有前面使用了__devinit和__devexit，我们还是先来讲讲这个：在Linux内核中，使用了大量不同的宏来标记具有不同作用的函数和数据结构，这些宏在include/linux/init.h头文件中定义，编译器通过这些宏可以把代码优化放到合适的内存位置，以减少内存占用和提高内核效率。__devinit、__devexit就是这些宏之一，在probe()和remove()函数中应该使用__devinit和__devexit宏。又当remove()函数使用了__devexit宏时，则在驱动结构体中一定要使用__devexit_p宏来引用remove()，所以下面就用__devexit_p来引用rtc_remove*/

static struct platform_driver s3c2410wdt_driver = {
	.probe		= s3c2410wdt_probe,
	.remove		= __devexit_p(s3c2410wdt_remove),
	.shutdown	= s3c2410wdt_shutdown,
	.suspend	= s3c2410wdt_suspend,
	.resume		= s3c2410wdt_resume,
	.driver		= {
		.owner	= THIS_MODULE,
		.name	= "s3c2410-wdt", 
              /*注意这里的名称一定要和系统中定义平台设备的名称一致，这样才能把平台设备与该平台设备的驱动关联起来*/
	},
};


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

static int __init watchdog_init(void)
{
	printk(banner);
	return platform_driver_register(&s3c2410wdt_driver);
}

static void __exit watchdog_exit(void)
{
	platform_driver_unregister(&s3c2410wdt_driver);
}

module_init(watchdog_init);
module_exit(watchdog_exit);

MODULE_AUTHOR("Ben Dooks <[email protected]>, "
	      "Dimitry Andric <[email protected]>");
MODULE_DESCRIPTION("S3C2410 Watchdog Device Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);
MODULE_ALIAS("platform:s3c2410-wdt");

配置内核，默认情况下已经配置

Devide drivers --->

       <*> Watchdog Timer Support --->

              <*> s3c2410 wathcdog

测试：

      我们可以使用echo向/dev/watchdog设备随便写入一些数据即可开启看门狗，比如：echo 0 > /dev/watchdog如果等待15秒钟，系统自动重启。

      由驱动程序知道，只要写入“V”就可以停止看门狗，echo –n V > /dev/watchdog，-n是去掉回车。

 

下面是一个图形化各个主要函数之间层次关系，更清晰的了解驱动程序。

module_init(&s3c24xx_i2c_driver)

       |__ platform_driver_register(&s3c24xx_i2c_driver)

                     |__ s3c24xx_i2c_probe

                     |        |__ platform_get_resource   

                     |        |__ request_irq

                     |        |__ misc_register(&s3c2410wdt_miscdev)

                     |               |__ &s3c2410wdt_fops

                     |                      |__ s3c2410wdt_open

                     |                      |__ s3c2410wdt_release

                     |                      |__ s3c2410wdt_write

                     |                      |__ s3c2410wdt_ioctl

                     |                      |__ no_llseek

                     |__ s3c2410wdt_remove

                     |__ s3c2410wdt_shutdown

                     |__ s3c2410wdt_suspend

                     |__ s3c2410wdt_resume

module_exit(watchdog_exit)

       |__ platform_driver_unregister(&s3c2410wdt_driver)