mini6410 看门狗源码分析

转自： http://blog.csdn.net/muge0913/article/details/7067072

 

mini6410 看门狗源码分析

 看门狗代码放在linux/drivers/char/watchdog/s3c2410_wdt.c中分析如下：
 仅供技术参考，转载请注明出处：http://write.blog.csdn.net/postedit/7067072
 /* linux/drivers/char/watchdog/s3c2410_wdt.c
  *
  * Copyright (c) 2004 Simtec Electronics
  *  Ben Dooks <[email protected]>
  *
  * S3C2410 Watchdog Timer Support
  *
  * Based on, softdog.c by Alan Cox,
  *     (c) Copyright 1996 Alan Cox <[email protected]>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

 #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 <linux/cpufreq.h>
 #include <linux/slab.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)
 /*
 *nowayout表示决不允许看门狗关闭，为1表示不允许关闭，为0表示允许关闭；
 *tmr_margin表示默认的看门狗喂狗时间为15s；
 *tmr_atboot表示系统启动时就使能看门狗，为1表示使能，为0表示关闭；
 *soft_noboot表示看门狗工作的方式，看门狗可以作为定时器使用也可作为复位硬件使用，
 *soft_noboot为1表示看门狗作为定时器使用，不发送复位信号；
 *debug表示是否使用调试模式来调试代码，该模式中，会打印调试信息。
 */
 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);

 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 0)");
 MODULE_PARM_DESC(debug, "Watchdog debug, set to >1 for debug (default 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)
 {
     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)
 {
     spin_lock(&wdt_lock);
     __s3c2410wdt_stop();
     spin_unlock(&wdt_lock);
 }

 static void s3c2410wdt_start(void)
 {
     unsigned long wtcon;

     spin_lock(&wdt_lock);
     /*首先停止看门狗*/
     __s3c2410wdt_stop();
     /*读看门狗的控制寄存器*/
     wtcon = readl(wdt_base + S3C2410_WTCON);
     /*使能看门狗，设置时钟分频值为128*/
     wtcon |= S3C2410_WTCON_ENABLE | S3C2410_WTCON_DIV128;
     /*上边说过看门狗一个作为一个正常的16位内部定时器也可作为复位硬件*/
     if (soft_noboot) {//如果作为内部定时器
         wtcon |= S3C2410_WTCON_INTEN;//开中断使能
         wtcon &= ~S3C2410_WTCON_RSTEN;//关闭复位使能
     } else {//如果作为复位硬件
         wtcon &= ~S3C2410_WTCON_INTEN;//关闭中断使能
         wtcon |= S3C2410_WTCON_RSTEN;//开复位使能
     }

     DBG("%s: wdt_count=0x%08x, wtcon=%08lx\n",
         __func__, wdt_count, wtcon);
 /*这里为什么要设置WTCNT的值，不是WTDAT中的值自动载入WTCNT吗？看看datasheet就知道了，看门狗定时器最初
 *使能的时候，WTDAT寄存器的值不会自动载入时        间计数器，所以WTCNT寄存器必须在使能它之前设置一个初始值
 */
     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 inline int s3c2410wdt_is_running(void)
 {
     return readl(wdt_base + S3C2410_WTCON) & S3C2410_WTCON_ENABLE;
 }

 static int s3c2410wdt_set_heartbeat(int timeout)
 {
     /*首先获得看门狗的时钟*/
     unsigned long freq = clk_get_rate(wdt_clock);
     unsigned int count;
     unsigned int divisor = 1;
     unsigned long wtcon;

     if (timeout < 1)
         return -EINVAL;

     freq /= 128;
     /*秒数乘以每秒的时间滴答等于计数值*/
     count = timeout * freq;

     DBG("%s: count=%d, timeout=%d, freq=%lu\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
     */
     /*计数值不能大于WTCNT的最大范围，WTCNT是一个16位的计数器，最大值是0x10000*/
     if (count >= 0x10000) {
         for (divisor = 1; divisor <= 0x100; divisor++) {
             if ((count / divisor) < 0x10000)
                 break;
         }
         /*未找到返回错误*/
         if ((count / divisor) >= 0x10000) {
             dev_err(wdt_dev, "timeout %d too big\n", timeout);
             return -EINVAL;
         }
     }

     /*看门狗的喂狗时间*/
     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 */
     //读看门狗的控制寄存器
     wtcon = readl(wdt_base + S3C2410_WTCON);
     //看门狗控制器高8位清零，也就是预分频部分清零
     wtcon &= ~S3C2410_WTCON_PRESCALE_MASK;
     //填入预分频系数
     wtcon |= S3C2410_WTCON_PRESCALE(divisor-1);

     //填入计数值
     writel(count, wdt_base + S3C2410_WTDAT);
     //填入控制寄存器的值
     writel(wtcon, wdt_base + S3C2410_WTCON);

     return 0;
 }

 /*
  *  /dev/watchdog handling
  */

 static int s3c2410wdt_open(struct inode *inode, struct file *file)
 {
     /*检查open_lock的第0位，如果open_lock的第0位为0，则表示test_and_set_bit的返回值为0，
         表示wdt设备没有被其他进程打开，如果为1，表示被其他进程打开，返回EBUSY*/
     if (test_and_set_bit(0, &open_lock))
         return -EBUSY;


     /*如果决不允许关闭看门狗，增加引用计数*/
     if (nowayout)
         __module_get(THIS_MODULE);
     /*设为不允许关闭*/
     expect_close = 0;

     /* start the timer */
     /*开启看门狗*/
     s3c2410wdt_start();
     /*这些寄存器不需要像文件一样对位置进行寻址*/
     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 (expect_close == 42)//看门狗为允许关闭状态
         s3c2410wdt_stop();//关闭看门狗
     else {
         dev_err(wdt_dev, "Unexpected close, not stopping watchdog\n");
         s3c2410wdt_keepalive();//否则喂狗
     }
     expect_close = 0; //设为不允许关闭
     clear_bit(0, &open_lock);//将open_lock的第0位设为0，是原子操作
     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) {//有数据写入len不为0
         if (!nowayout) {//允许关闭
             size_t i;

             /* In case it was set long ago */
             expect_close = 0; //关闭允许关闭状态

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

                 if (get_user(c, data + i))
                     return -EFAULT;
                 if (c == 'V')//如果向设备写入'V'，就允许关闭设
                     expect_close = 42;
             }
         }
         s3c2410wdt_keepalive();
     }
     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",
 };


 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://获得看门狗设备的信息
         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://对看门狗进行喂狗
         s3c2410wdt_keepalive();
         return 0;
     case WDIOC_SETTIMEOUT://设置看门狗的超时时间
         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 */
 /*
 *看门狗驱动作为字符驱动的file_operations结构
 */
 static const struct file_operations s3c2410wdt_fops = {
     .owner      = THIS_MODULE,
     .llseek     = no_llseek,
     .write      = s3c2410wdt_write,
     .unlocked_ioctl = s3c2410wdt_ioctl,
     .open       = s3c2410wdt_open,
     .release    = s3c2410wdt_release,
 };

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

 /* interrupt handler code */
 /*
 *如果选择了看门狗作为内部定时器，则当计数值为0时调用中断处理函数，中断处理函数的主要功能就是喂狗
 */
 static irqreturn_t s3c2410wdt_irq(int irqno, void *param)
 {
     dev_info(wdt_dev, "watchdog timer expired (irq)\n");
     /*中断处理中调用喂狗*/
     s3c2410wdt_keepalive();
     return IRQ_HANDLED;
 }


 #ifdef CONFIG_CPU_FREQ

 static int s3c2410wdt_cpufreq_transition(struct notifier_block *nb,
                       unsigned long val, void *data)
 {
     int ret;

     if (!s3c2410wdt_is_running())
         goto done;

     if (val == CPUFREQ_PRECHANGE) {
         /* To ensure that over the change we don't cause the
          * watchdog to trigger, we perform an keep-alive if
          * the watchdog is running.
          */

         s3c2410wdt_keepalive();
     } else if (val == CPUFREQ_POSTCHANGE) {
         s3c2410wdt_stop();

         ret = s3c2410wdt_set_heartbeat(tmr_margin);

         if (ret >= 0)
             s3c2410wdt_start();
         else
             goto err;
     }

 done:
     return 0;

  err:
     dev_err(wdt_dev, "cannot set new value for timeout %d\n", tmr_margin);
     return ret;
 }

 static struct notifier_block s3c2410wdt_cpufreq_transition_nb = {
     .notifier_call  = s3c2410wdt_cpufreq_transition,
 };

 static inline int s3c2410wdt_cpufreq_register(void)
 {
     return cpufreq_register_notifier(&s3c2410wdt_cpufreq_transition_nb,
                      CPUFREQ_TRANSITION_NOTIFIER);
 }

 static inline void s3c2410wdt_cpufreq_deregister(void)
 {
     cpufreq_unregister_notifier(&s3c2410wdt_cpufreq_transition_nb,
                     CPUFREQ_TRANSITION_NOTIFIER);
 }

 #else
 static inline int s3c2410wdt_cpufreq_register(void)
 {
     return 0;
 }

 static inline void s3c2410wdt_cpufreq_deregister(void)
 {
 }
 #endif



 /* device interface */

 static int __devinit s3c2410wdt_probe(struct platform_device *pdev)
 {
     struct resource *res;
     struct device *dev;
     unsigned int wtcon;
     int started = 0;
     int ret;
     int size;

     DBG("%s: probe=%p\n", __func__, pdev);
     /*平台设备中的设备结构体device*/
     dev = &pdev->dev;
     wdt_dev = &pdev->dev;

     /* get the memory region for the watchdog timer */
      /*获得看门狗的内存资源*/
     res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
     /*获取失败则推出*/
     if (res == NULL) {
         dev_err(dev, "no memory resource specified\n");
         return -ENOENT;
     }
     /*内存资源所占的字节数*/
     size = resource_size(res);
     /*申请一块IO内存，对应看门狗的3个寄存器*/
     wdt_mem = request_mem_region(res->start, size, pdev->name);
     if (wdt_mem == NULL) {
         dev_err(dev, "failed to get memory region\n");
         return -EBUSY;
     }
     /*获得虚拟地址*/
     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);
     /*申请中断*/
     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;
     }

     /*并注册中断处理函数*/
     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;
     }
     /*获得看门狗时钟*/
     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;
     }
     /*时钟使能*/
     clk_enable(wdt_clock);

     if (s3c2410wdt_cpufreq_register() < 0) {
         printk(KERN_ERR PFX "failed to register cpufreq\n");
         goto err_clk;
     }

     /* see if we can actually set the requested timer margin, and if
      * not, try the default value */
     /*设置看门狗复位时间，如果成功返回0*/
     if (s3c2410wdt_set_heartbeat(tmr_margin)) {
         /*如果不成功，看门狗的复位时间设置成默认值*/
         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");
     }
     /*注册混杂设备*/
     ret = misc_register(&s3c2410wdt_miscdev);
     if (ret) {
         dev_err(dev, "cannot register miscdev on minor=%d (%d)\n",
             WATCHDOG_MINOR, ret);
         goto err_cpufreq;
     }
     /*如果开机的时候就启动看门狗*/
     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();//关闭看门狗
     }

     /* print out a statement of readiness */
     /*读出看门狗控制寄存器的值*/
     wtcon = readl(wdt_base + S3C2410_WTCON);
     /*打印看门狗是否使能，是否允许发出复位信号，是否允许发出中断信号*/
     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_cpufreq:
     s3c2410wdt_cpufreq_deregister();

  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)
 {
     misc_deregister(&s3c2410wdt_miscdev);//注销混杂设备

     s3c2410wdt_cpufreq_deregister();

     clk_disable(wdt_clock);//关闭时钟
     clk_put(wdt_clock);//减少时钟引用计数
     wdt_clock = NULL;

     free_irq(wdt_irq->start, dev);//释放中断号
     wdt_irq = NULL;

     iounmap(wdt_base);//关闭内存映射

     release_resource(wdt_mem);//释放平台资源
     kfree(wdt_mem);//释放I/O内存
     wdt_mem = NULL;
     return 0;
 }

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

 #ifdef CONFIG_PM

 static unsigned long wtcon_save;
 static unsigned long wtdat_save;
 /*
 *平台驱动中的电源管理部分
 */
 static int s3c2410wdt_suspend(struct platform_device *dev, pm_message_t state)
 {
     /* Save watchdog state, and turn it off. */
     /*只要保存S3C2410_WTDAT就可以了，不需要保存S3C2410_WTCNT，
     *S3C2410_WTCNT的值会在系统还原的时候直接赋为S3C2410_WTDAT中的值
     */
     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 */

 /*
 *S3C2410的看门狗同时具有多重身份：字符设备，混杂设备，平台设备。
 *下面是看门狗驱动作为平台驱动的描述：
 */
 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",
     },
 };


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


 /*
 *看门狗驱动作为平台驱动的注册
 */
 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");