ARM-Linux驱动--Watch Dog Timer(看门狗)驱动分析

 

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。