Linux的WDT(watchdog)驅動

第一部分： WDT驅動原理
WDT在內核中通常都實現為misc驅動。
WDT介紹
一個Watchdog Timer（WDT）是一個在軟件出錯的時候可以復位計算機系統的硬件電路。
通 常一個用戶空間守護進程會在正常的時間間隔內通過/dev/watchdog特殊設備文件來通知內核的watchdog驅動，用戶空間仍然正常。當這樣的 一個通知發生時，驅動通常會告訴硬件watchdog一切正常，然後watchdog應該再等待一段時間來復位系統。如果用戶空間出問題（RAM錯誤，內 核bug等），則通知將會停止，然後硬件watchdog將在超時後復位系統。
Linux的watchdog API是一個相當特別的東西，不同的驅動實現是不同的，而且有時部分是不兼容的。這個文檔正是要嘗試著去說明已經出現的用法，並且使以後的驅動作者把它作為一份參考。
最簡單的 API:
所 有的設備驅動都支持的基本的操作模式，一旦/dev/watchdog被打開，則watchdog激活，並且除非喂狗，否則將在一段時間之後重啟，這個時 間被稱為timeout或margin。最簡單的喂狗方法就是寫一些數據到設備。一個非常簡單的watchdog守護進程看起來就像這個文件這樣：
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;
}

一個高級一些的驅動在喂狗之前，可能還會做一些其他的事情，比如說檢查HTTP服務器是否依然可以相應。
當 設備關閉的時候，除非支持"Magic Close"特性。否則watchdog被關閉。這並不總是一個好主意，比如watchdog守護進程出現了bug並且崩潰了，則系統將不會重啟。因此， 某些驅動支持"Disable watchdog shutdown on close", CONFIG_WATCHDOG_NOWAYOUT配置選項。當編譯內核的時候這個選項被設置為Y，則一旦watchdog被啟動，則將沒有辦法能夠停 止。這樣，則當watchdog守護進程崩潰的時候，系統仍將在超時後重啟。Watchdog設備常常也支持nowayout模塊參數，這樣這個選項就可 以在運行時進行控制。
Magic Close 特性:
如果一個驅動支持"Magic Close"，則除非在關閉文件前，魔幻字符'V'被發送到/dev/watchdog，驅動將不停止watchdog。如果用戶空間守護進程在關閉文件前沒有發送這個字符，則驅動認為用戶空間崩潰，並在關閉watchdog前停止喂狗。
這樣的話，如果沒有在一定的時間內重新打開watchdog，則將導致一個重啟。
ioctl API:
所有標准的驅動也應該支持一個ioctl API。
喂狗使用一個ioctl：
所有的驅動都有一個ioctl接口支持至少一個ioctl命令，KEEPALIVE。這個 ioctl 做的事和一個寫watchdog設備完全一樣，所以，上面程序的主循環可以替換為：
while (1) {

ioctl(fd, WDIOC_KEEPALIVE, 0);

sleep(10);

}

ioctl的參數被忽略。
設置和獲得超時值：
對 於某些驅動來說，在上層使用SETTIMEOUT ioctl命令改變watchdog的超時值是可能的，那些驅動在他們的選項與中有WDIOF_SETTIMEOUT標志。參數是一個代表以秒為單位的超 時值，驅動將在同一個變量中返回實際使用的超時值，這個超時值可能由於硬件的限制，而不同於所請求的超時值
int timeout = 45;
ioctl(fd, WDIOC_SETTIMEOUT, &timeout);
printf("The timeout was set to %d seconds\n", timeout);
如果設備的超時值的粒度只能到分鐘，則這個例子可能實際打印"The timeout was set to 60 seconds"。
自從Linux 2.4.18內核，通過GETTIMEOUT ioctl命令查詢當前超時值也是可能的：
ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
printf("The timeout was is %d seconds\n", timeout);
預處理：
Pretimeouts:
一些watchdog定時器，可以被設置為，在他們實際復位系統前，有一個觸發。這可能通過一個NMI，中斷，或其他機制。這將允許在它復位系統前Linux去記錄一些有用的信息（比如panic信息和內核轉儲）。
pretimeout = 10;
ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout);
注意，預超時值應該是一個相對於超時值提前的秒數。而不是直到預超時的秒數。
比如，如果你設置超時值為60秒，預超時值為10秒，那麼預超時將在50秒後到達。設置為0則是禁用它。預超時還有一個get功能：
ioctl(fd, WDIOC_GETPRETIMEOUT, &timeout);
printf("The pretimeout was is %d seconds\n", timeout);
不是所有的watchdog驅動都支持一個預超時的。
獲得重啟前的秒數
一些watchdog驅動有一個報告在重啟前的剩余時間的功能。WDIOC_GETTIMELEFT就是返回重啟前的秒數的ioctl命令。
ioctl(fd, WDIOC_GETTIMELEFT, &timeleft);
printf("The timeout was is %d seconds\n", timeleft);
環境監視：
Environmental monitoring:
所有的watchdog驅動都被要求返回更多關於系統的信息，有些返回溫度，風扇和功率水平監測，依稀可以告訴你上一次重啟系統的原因。GETSUPPORT ioctl可以用來查詢設備可以做什麼：
struct watchdog_info ident;
ioctl(fd, WDIOC_GETSUPPORT, &ident);
ident結構中返回的字段是：
identity 一個標識watchdog驅動的字符串
firmware_version 如果可用的話，就是卡的固件版本
options 一個描述設備支持什麼的標志
options字段可以有下面的位集，和描述GET_STATUS 和 GET_BOOT_STATUS ioctls可以返回什麼種類的信息。
第二部分： WDT驅動源碼
驅動架構比較簡單，由於kernel啟動時，定義並加入了watchdog的platform_device,所以驅動定義並注冊watchdog 的platform_driver
/* 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 <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 to do (and if) 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 in if 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;

/* In case 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;

//請求分配指定的I/O內存資源
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;
}

//將一個IO地址空間映射到內核的虛擬地址空間上去，便於訪問
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;
}

//注冊中斷服務函數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;
}

//從平台時鐘隊列中獲取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, and if
* 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();
} 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");

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 與 platform_device s3c_device_wdt 對應
*s3c_device_wdt 在arch/arm/plat-s3c24xx/devs.c中定義
*兩者的工作順序是先定義platform_device -> 注冊 platform_device->
*在mini2440_machine_init()中完成
*再定義 platform_driver-> 注冊 platform_driver
*/
static struct platform_driver s3c2410wdt_driver = {
.probe = s3c2410wdt_probe, //設備的檢測，所以需要先注冊設備
.remove = __devexit_p(s3c2410wdt_remove), //刪除該設備
.shutdown = s3c2410wdt_shutdown, //關閉該設備
.suspend = s3c2410wdt_suspend,
.resume = s3c2410wdt_resume,
.driver = { //設備驅動
.owner = THIS_MODULE,
/*
*對應 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) //模塊初始化
{
printk(banner); //打印信息
return platform_driver_register(&s3c2410wdt_driver); //注冊設備的驅動程序
}

static void __exit watchdog_exit(void) //移除模塊
{
platform_driver_unregister(&s3c2410wdt_driver); //unregister a driver for platform-level devices
}

module_init(watchdog_init);
module_exit(watchdog_exit);

MODULE_AUTHOR("Ben Dooks , "
"Dimitry Andric ");
MODULE_DESCRIPTION("S3C2410 Watchdog Device Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);
MODULE_ALIAS("platform:s3c2410-wdt");