ARM-Linux驱动--Watch Dog Timer(看门狗)驱动分析

硬件平台：FL2440

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 <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/regs-gpio.h> #include <mach/map.h> #undef S3C_VA_WATCHDOG #define S3C_VA_WATCHDOG (0) #include <asm/plat-s3c/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 = 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);
设置默认不是重启机器，而是执行中断函数，当不喂狗，计数器减到0，点亮LED，然后喂狗，重新计数。