蜕变成蝶~Linux设备驱动之watchdog设备驱动

提示：扫一扫查出行
【扫一扫了解最新限行尾号】
复制提示

看门狗（watchdog ）分硬件看门狗和软件看门狗。硬件看门狗是利用一个定时器电路，其定时输出连接到电路的复位端，程序在一定时间范围内对定时器清零（俗称 “喂狗”），如果程序出现故障，不在定时周期内复位看门狗，就使得看门狗定时器溢出产生复位信号并重启系统。软件看门狗原理上一样，只是将硬件电路上的定时器用处理器的内部定时器代替。

1 看门狗的三个寄存器

1.1 watchdog原理

S3C2410内部集成了watchdog，提供3 个寄存器对watchdog 进行操作，这3 个寄存器分别为WTCON （watchdog 控制寄存器）、WTDAT （watchdog 数据寄存器）和WTCNT(watchdog 记数寄存器) S3c2440的看门狗的原理框图如下：

可以看到，看门狗定时器的频率由PCLK提供，其预分频器最大取值为255+1；另外，通过MUX，可以进一步降低频率。定时器采用递减模式，一旦到0，则可以触发看门狗中断以及RESET复位信号。看门狗定时器的频率的计算公式如下：

t_watchdog = 1/[PCLK/(Prescaler value + 1)/Division_factor]

1.2 开启S3C2410 的看门狗

void enable watchdog ()
{ rWTCON = WTCON DIV64 | WTCON RSTEN;//64分频、开启复位信号
rWTDAT = 0x8000;//计数目标 rWTCON |= WTCON ENABLE;//开启看门狗
}

1.3 S3C2410 的看门狗 “喂狗”

void feed dog ()
{
rWTCNT=0x8000;
}

1.4 看门狗的使用例程

void main () { init system (); ... enable watchdog ();//启动看门狗 ... while (1) { ... feed dog (); //喂狗 } }

2 watchdog中的数据结

有一类设备被称为 “平台设备”，通常 SoC 系统中集成的独立的外设单元都被当作平台设备处理

2.1 platform_device 结构体

struct platform device { const char * name;//设备名 u32 id; struct device dev; u32 num resources;//设备所使用各类资源数量 struct resource * resource;//资源 };

2.2 S3C2410 中的平台设备

struct platform device *s3c24xx uart devs[];
struct platform device s3c device usb; //USB 控制器 struct platform device s3c device lcd; //LCD 控制器 struct platform device s3c device wdt; //看门狗
2 struct platform device s3c device i2c; //I C 控制器 struct platform device s3c device iis; //IIS struct platform device s3c device rtc; //实时钟
... /*SMDK2410开发板使用的平台设备*/ static struct platform device *smdk2410 devices[] initdata = { &s3c device usb, //USB &s3c device lcd, //LCD &s3c device wdt, //看门狗 &s3c device i2c, //I C &s3c device iis, //IIS };

2.3 S3C2410 看门狗的platform_device 结构体

struct platform device s3c device wdt = { .name = "s3c2410-wdt", //设备名 .id = - 1, . num resources = ARRAY SIZE (s3c wdt resource), //资源数量 .resource = s3c wdt resource, //看门狗所使用资源 };

2.4 int platform_add_devices()函数

int platform add devices(struct platform device **devs, int num) { int i, ret = 0; for (i = 0; i < num; i++) {
ret = platform device register(devs[i]);/*注册平台设备*/ if (ret) /*注册失败*/ { while (--i >= 0) platform device unregister(devs[i]);/*注销已经注册的平台设备 */ break; } } return ret; }

2.5 platform_driver 结构体

struct platform driver
{ int (*probe)(struct platform device *);//探测 int (*remove)(struct platform device *);//移除 void (*shutdown)(struct platform device *);//关闭 int (*suspend)(struct platform device *, pm message t state);// 挂起 int (*resume)(struct platform device *);//恢复 struct device driver driver; };

2.6 S3C2410 看门狗的platform_driver 结构体

static struct platform driver s3c2410wdt driver = { .probe = s3c2410wdt probe,//S3C2410看门狗探测 .remove = s3c2410wdt remove,// S3C2410看门狗移除 .shutdown = s3c2410wdt shutdown,//S3C2410看门狗关闭 .suspend = s3c2410wdt suspend,//S3C2410看门狗挂起 .resume = s3c2410wdt resume, //S3C2410看门狗恢复 .driver = { .owner = THIS MODULE, .name = "s3c2410-wdt",//设备名 },
}；

2.7 S3C2410 看门狗所用资源

static struct resource s3c wdt resource[] = { [0] = { .start = S3C24XX PA WATCHDOG, //看门狗I/O 内存开始位置 .end = S3C24XX PA WATCHDOG + S3C24XX SZ WATCHDOG - 1, //看门狗I/O 内存结束位置 .flags = IORESOURCE MEM, //I/O 内存资源 } , [1] = { .start = IRQ WDT, //看门狗开始IRQ 号 .end = IRQ WDT, //看门狗结束IRQ 号 .flags = IORESOURCE IRQ, //IRQ 资源 } };

2.8 S3C2410 看门狗驱动的miscdevice 结构体

static struct miscdevice s3c2410wdt miscdev =
{ .minor = WATCHDOG MINOR,//次设备号 .name = "watchdog", .fops = &s3c2410wdt fops,//文件操作结构体 };

2.9 S3C2410 看门狗驱动的文件操作结构体

static struct file operations s3c2410wdt fops =
{ .owner = THIS MODULE, .llseek = no llseek, //seek .write = s3c2410wdt write, //写函数 .ioctl = s3c2410wdt ioctl, //ioctl 函数 .open = s3c2410wdt open, //打开函数 .release = s3c2410wdt release,//释放函数 };

3 加载和卸载函数

驱动模块的加载和卸载函数分别用 platform_driver_register() 和 platform_driver_ unregister()注册和注销platform_driver

3.1 S3C2410 看门狗驱动

static int __init watchdog__init (void)
{
printk (banner); return platform driver register(&s3c2410wdt driver);// 注册platform driver
} static void exit watchdog exit (void)
{
platform driver unregister (&s3c2410wdt driver);// 注销 platform driver
}

4 探测和移除函数

4.1 探测函数

static int s3c2410wdt probe (struct platform device *pdev)
{
struct resource *res;
int started = 0;
int ret;
int size; DBG ("%s: probe=%p\n", _ _FUNCTION_ _, pdev); /* 获得看门狗的内存区域 */ res = platform get resource (pdev, IORESOURCE MEM, 0);
if (res == NULL)
{ printk(KERN INFO PFX "failed to get memory region resouce\n");
return - ENOENT;
} size = (res->end - res->start) + 1;
//申请I/O 内存 wdt mem = request mem region (res->start, size, pdev->name); if (wdt mem == NULL)
{ printk(KERN INFO PFX "failed to get memory region\n");
return - ENOENT;
} wdt base = ioremap (res->start, size); //设备内存->虚拟地址 if (wdt base == 0)
{ printk(KERN INFO PFX "failed to ioremap () region\n");
return - EINVAL;
} DBG ("probe: mapped wdt base=%p\n", wdt base); /* 获得看门狗的中断 */ res = platform get resource (pdev, IORESOURCE IRQ, 0);
if (res == NULL)
{ printk(KERN INFO PFX "failed to get irq resource\n");
return - ENOENT;
}
//申请中断 ret = request irq (res->start, s3c2410wdt irq, 0, pdev->name,
pdev);
if (ret != 0)
{ printk(KERN INFO PFX "failed to install irq (%d)\n", ret);
return ret;
} wdt clock = clk get (&pdev->dev, "watchdog"); //获得看门狗时钟源 if (wdt clock == NULL)
{ printk(KERN INFO PFX "failed to find watchdog clock source\n");
return - ENOENT;
} clk enable (wdt clock); /* 看看是否能设置定时器的超时时间为期望的值，如果不能，使用缺省值 */ if (s3c2410wdt set heartbeat (tmr margin))
{ started = s3c2410wdt set heartbeat ( CONFIG S3C2410 WATCHDOG DEFAULT TIME);
if (started == 0)
{ printk (KERN INFO PFX "tmr margin value out of range, default
%d used\n",CONFIG S3C2410 WATCHDOG DEFAULT TIME);
}
else
{ printk (KERN INFO PFX
"default timer value is out of range, cannot start\n");
}
} //注册miscdevice ret = misc register(&s3c2410wdt miscdev);
if (ret)
{ printk(KERN ERR PFX "cannot registermiscdev on minor=%d (%d)\n", WATCHDOG MINOR, ret);
return ret;
} if (tmr atboot && started == 0)
{ printk(KERN INFO PFX "Starting Watchdog Timer\n"); s3c2410wdt start ();
} return 0;
}

4.2 探测函数

static int s3c2410wdt remove (struct platform device *dev) { if (wdt mem != NULL) { release resource (wdt mem); //释放资源 kfree (wdt mem);//释放内存 wdt mem = NULL; } //释放中断 if (wdt irq != NULL) { free irq (wdt irq->start, dev); wdt irq = NULL;
} //禁止时钟源 if (wdt clock != NULL) { clk disable (wdt clock); clk put (wdt clock); wdt clock = NULL; }
misc deregister(&s3c2410wdt miscdev);//注销miscdevice return 0; }

5 挂起和恢复函数

5.1 挂起函数

static int s3c2410wdt suspend (struct platform device *dev, pm message t state)
{
/* 保存看门狗状态，停止它 */ wtcon save = readl (wdt base + S3C2410 WTCON); wtdat save = readl (wdt base + S3C2410 WTDAT); s3c2410wdt stop (); return 0;
}

5.2 恢复函数

static int s3c2410wdt resume (struct platform device *dev)
{
/* 恢复看门狗状态 */ writel (wtdat save, wdt base + S3C2410 WTDAT); writel (wtdat save, wdt base + S3C2410 WTCNT); writel (wtcon save, wdt base + S3C2410 WTCON); printk (KERN INFO PFX "watchdog %sabled\n", (wtcon save &S3C2410 WTCON ENABLE)? "en" : "dis"); return 0;
}

6 打开和释放函数

6.1 打开函数

static int s3c2410wdt open (struct inode *inode, struct file *file)
{ if (down trylock (&open lock)) //获得打开锁
return - EBUSY; if (nowayout)
{ module get (THIS MODULE);
}
else
{ allow close = CLOSE STATE ALLOW;
} /* 启动看门狗 */ s3c2410wdt start (); return nonseekable open (inode, file);
}

6.2 释放函数

static int s3c2410wdt release (struct inode *inode,struct file *file)
{
/* 停止看门狗 */ if (allow close == CLOSE STATE ALLOW)
{ s3c2410wdt stop ();
}
else
{ printk (KERN CRIT PFX "Unexpected close, not stopping
watchdog!\n"); s3c2410wdt keepalive ();
} allow close = CLOSE STATE NOT; up (&open lock); //释放打开锁
return 0;
}

7 启停watchdog函数和写函数

7.1 启停看门狗函数

/*停止看门狗*/ static int s3c2410wdt stop (void)
{
unsigned long wtcon; wtcon = readl(wdt base + S3C2410 WTCON);
//停止看门狗，禁止复位 wtcon &= ~ (S3C2410 WTCON ENABLE | S3C2410 WTCON RSTEN); writel (wtcon, wdt base + S3C2410 WTCON); return 0;
} /*开启看门狗*/ static int s3c2410wdt start (void)
{
unsigned long wtcon; s3c2410wdt stop (); wtcon = readl(wdt base + S3C2410 WTCON);
//使能看门狗，128 分频 wtcon |= S3C2410 WTCON ENABLE | S3C2410 WTCON DIV128; if (soft noboot)
{ wtcon |= S3C2410 WTCON INTEN; //使能中断 wtcon &= ~S3C2410 WTCON RSTEN; //禁止复位
}
else
{ wtcon &= ~S3C2410 WTCON INTEN; //禁止中断 wtcon |= S3C2410 WTCON RSTEN; //使能复位
} DBG ("%s: wdt count=0x%08x, wtcon=%08lx\n", FUNCTION , wdt count, wtcon); writel (wdt count, wdt base + S3C2410 WTDAT); writel (wdt count, wdt base + S3C2410 WTCNT); writel (wtcon, wdt base + S3C2410 WTCON); return 0;
}

7.2 写函数

static ssize t s3c2410wdt write (struct file *file, const char user *data, size t len, loff t *ppos)
{
/* 刷新看门狗 */
if (len)
{
if (!nowayout)
{ size t i; allow close = CLOSE STATE NOT;
for (i = 0; i != len; i++)
{
char c; if (get user(c, data + i))//用户空间->内核空间
return - EFAULT;
if (c == 'V ') //如果写入了'V ' ，允许关闭 allow close = CLOSE STATE ALLOW;
}
} s3c2410wdt keepalive ();
}
return len;
}