RM-Linux驱动--Watch Dog Timer(看门狗)驱动分析

from：/article/1393236.html

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

[cpp] view plaincopy

#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。