Linux驱动学习之：WDT(watchdog)驱动

第一部分： WDT驱动原理

WDT在内核中通常都实现为misc驱动。

WDT介绍

一个Watchdog Timer（WDT）是一个在软件出错的时候可以复位计算机系统的硬件电路。

通常一个用户空间守护进程会在正常的时间间隔内通过/dev/watchdog特殊设备文件来通知内核的watchdog驱动，用户空间仍然正常。当这样的一个通知发生时，驱动通常会告诉硬件watchdog一切正常，然后watchdog应该再等待一段时间来复位系统。如果用户空间出问题（RAM错误，内核bug等），则通知将会停止，然后硬件watchdog将在超时后复位系统。

Linux的watchdog API是一个相当特别的东西，不同的驱动实现是不同的，而且有时部分是不兼容的。这个文档正是要尝试着去说明已经出现的用法，并且使以后的驱动作者把它作为一份参考。

最简单的 API:

所有的设备驱动都支持的基本的操作模式，一旦/dev/watchdog被打开，则watchdog激活，并且除非喂狗，否则将在一段时间之后重启，这个时间被称为timeout或margin。最简单的喂狗方法就是写一些数据到设备。一个非常简单的watchdog守护进程看起来就像这个文件这样：

Documentation/watchdog/src/watchdog-simple.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
int main(void)
{
int fd = open("/dev/watchdog", O_WRONLY);
int ret = 0;
if(fd ==-1){
perror("watchdog");
exit(EXIT_FAILURE);
}
while(1){
ret = write(fd,"\0", 1);
if(ret != 1){
ret =-1;
break;
}
ret = fsync(fd);
if(ret)
break;
sleep(10);
}
close(fd);
return ret;
}

一个高级一些的驱动在喂狗之前，可能还会做一些其他的事情，比如说检查HTTP服务器是否依然可以相应。

当设备关闭的时候，除非支持"Magic Close"特性。否则watchdog被关闭。这并不总是一个好主意，比如watchdog守护进程出现了bug并且崩溃了，则系统将不会重启。因此，某些驱动支持"Disable watchdog shutdown on close", CONFIG_WATCHDOG_NOWAYOUT配置选项。当编译内核的时候这个选项被设置为Y，则一旦watchdog被启动，则将没有办法能够停止。这样，则当watchdog守护进程崩溃的时候，系统仍将在超时后重启。Watchdog设备常常也支持nowayout模块参数，这样这个选项就可以在运行时进行控制。

Magic Close 特性:

如果一个驱动支持"Magic Close"，则除非在关闭文件前，魔幻字符'V'被发送到/dev/watchdog，驱动将不停止watchdog。如果用户空间守护进程在关闭文件前没有发送这个字符，则驱动认为用户空间崩溃，并在关闭watchdog前停止喂狗。

这样的话，如果没有在一定的时间内重新打开watchdog，则将导致一个重启。

ioctl API:

所有标准的驱动也应该支持一个ioctl API。

喂狗使用一个ioctl：

所有的驱动都有一个ioctl接口支持至少一个ioctl命令，KEEPALIVE。这个 ioctl 做的事和一个写watchdog设备完全一样，所以，上面程序的主循环可以替换为：

while(1){
ioctl(fd, WDIOC_KEEPALIVE, 0);
sleep(10);
}

ioctl的参数被忽略。

设置和获得超时值：

对于某些驱动来说，在上层使用SETTIMEOUT ioctl命令改变watchdog的超时值是可能的，那些驱动在他们的选项与中有WDIOF_SETTIMEOUT标志。参数是一个代表以秒为单位的超时值，驱动将在同一个变量中返回实际使用的超时值，这个超时值可能由于硬件的限制，而不同于所请求的超时值

int timeout = 45;

ioctl(fd, WDIOC_SETTIMEOUT, &timeout);

printf("The timeout was set to %d seconds\n", timeout);

如果设备的超时值的粒度只能到分钟，则这个例子可能实际打印"The timeout was set to 60 seconds"。

自从Linux 2.4.18内核，通过GETTIMEOUT ioctl命令查询当前超时值也是可能的：

ioctl(fd, WDIOC_GETTIMEOUT, &timeout);

printf("The timeout was is %d seconds\n", timeout);

预处理：

Pretimeouts:

一些watchdog定时器，可以被设置为，在他们实际复位系统前，有一个触发。这可能通过一个NMI，中断，或其他机制。这将允许在它复位系统前Linux去记录一些有用的信息（比如panic信息和内核转储）。

pretimeout = 10;

ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout);

注意，预超时值应该是一个相对于超时值提前的秒数。而不是直到预超时的秒数。

比如，如果你设置超时值为60秒，预超时值为10秒，那么预超时将在50秒后到达。设置为0则是禁用它。预超时还有一个get功能：

ioctl(fd, WDIOC_GETPRETIMEOUT, &timeout);

printf("The pretimeout was is %d seconds\n", timeout);

不是所有的watchdog驱动都支持一个预超时的。

获得重启前的秒数

一些watchdog驱动有一个报告在重启前的剩余时间的功能。WDIOC_GETTIMELEFT就是返回重启前的秒数的ioctl命令。

ioctl(fd, WDIOC_GETTIMELEFT, &timeleft);

printf("The timeout was is %d seconds\n", timeleft);

环境监视：

Environmental monitoring:

所有的watchdog驱动都被要求返回更多关于系统的信息，有些返回温度，风扇和功率水平监测，依稀可以告诉你上一次重启系统的原因。GETSUPPORT ioctl可以用来查询设备可以做什么：

struct watchdog_info ident;

ioctl(fd, WDIOC_GETSUPPORT, &ident);

ident结构中返回的字段是：

identity一个标识watchdog驱动的字符串

firmware_version如果可用的话，就是卡的固件版本

options一个描述设备支持什么的标志

options字段可以有下面的位集，和描述GET_STATUS 和 GET_BOOT_STATUS ioctls可以返回什么种类的信息。

第二部分： WDT驱动源码

驱动架构比较简单，由于kernel启动时，定义并加入了watchdog的platform_device,所以驱动定义并注册watchdog 的platform_driver

/* linux/drivers/char/watchdog/s3c2410_wdt.c
*
* Ben Dooks <ben@simtec.co.uk>
*
* S3C2410 Watchdog Timer Support
*
* Based on, softdog.c by Alan Cox,
*
* 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;ifnot, 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 <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);
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)");
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);
__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)
{
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 todo(andif) 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)
__module_get(THIS_MODULE);
expect_close = 0;
/* start the timer */
s3c2410wdt_start();
return nonseekable_open(inode, file);
}
static int s3c2410wdt_release(struct inode *inode, struct file *file)
{
/*
* Shut off the timer.
* Lock it inif 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){
size_t i;
/*Incase 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;
}
}
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:
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,
.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 */
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;
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 -- flags is IORESOURCE_MEM */
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;
//请求分配指定的I/O内存资源
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;
}
//将一个IO地址空间映射到内核的虚拟地址空间上去，便于访问
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);
/*get the memory region for the watchdog timer -- flags is IORESOURCE_IRQ */
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;
}
//注册中断服务函数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;
}
//从平台时钟队列中获取clk
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;
}
//inform the system when the clock source should be running
clk_enable(wdt_clock);
/* see if we can actually set the requested timer margin,andif
*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();
}elseif(!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
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 */
/*
*platform_driver s3c2410wdt_driver 与 platform_device s3c_device_wdt 对应
*s3c_device_wdt 在arch/arm/plat-s3c24xx/devs.c中定义
*两者的工作顺序是先定义platform_device -> 注册 platform_device->
*在mini2440_machine_init()中完成
*再定义 platform_driver-> 注册 platform_driver
*/
static struct platform_driver s3c2410wdt_driver ={
.probe = s3c2410wdt_probe,//设备的检测，所以需要先注册设备
.remove = __devexit_p(s3c2410wdt_remove),//删除该设备
.shutdown = s3c2410wdt_shutdown,//关闭该设备
.suspend = s3c2410wdt_suspend,
.resume= s3c2410wdt_resume,
.driver ={//设备驱动
.owner = THIS_MODULE,
/*
*对应 struct platform_device s3c_device_wdt = {
* .name = "s3c2410-wdt",
* ...
* };
*/
.name ="s3c2410-wdt",
},
};
static char banner[] __initdata =
KERN_INFO "S3C2410 Watchdog Timer, (c) 2004 Simtec Electronics\n";
static int __init watchdog_init(void)//模块初始化
{
printk(banner);//打印信息
return platform_driver_register(&s3c2410wdt_driver);//注册设备的驱动程序
}
static void __exit watchdog_exit(void)//移除模块
{
platform_driver_unregister(&s3c2410wdt_driver);//unregister a driver for platform-level devices
}
module_init(watchdog_init);
module_exit(watchdog_exit);
MODULE_AUTHOR("Ben Dooks <ben@simtec.co.uk>, "
"Dimitry Andric <dimitry.andric@tomtom.com>");
MODULE_DESCRIPTION("S3C2410 Watchdog Device Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);
MODULE_ALIAS("platform:s3c2410-wdt");

转载于:https://blog.51cto.com/dayu1980/1370762

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