S3C2440驱动篇—看门狗驱动分析

文章由LinuxBoy分享于2019-04-01 05:04:38热评（158）

S3C2440驱动篇—看门狗驱动分析

Linux-2.6.32.2内核自带S3C2440看门狗驱动，只需要配置一下就可以使用。驱动源代码位于drivers/watchdog/s3c2410_wdt.c，由于驱动使用了平台设备，有关平台设备学习参考这一篇文章。

驱动实现：

#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);
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) //喂狗
{
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) //停止看门狗
{
spin_lock(&wdt_lock);
__s3c2410wdt_stop();
spin_unlock(&wdt_lock);
}
static void s3c2410wdt_start(void) //启动看门狗
{
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) //根据timeout时间设置看门狗定时器初始值
{
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) /*nowayout是内涵配置选项，如果配置则看门狗不能被关闭*/
__module_get(THIS_MODULE);/*如果内核配置了CONFIG_WATCHDOG_NOWAYOUT项，则使模块使用计数加1*/
expect_close = 0;
/* start the timer */
s3c2410wdt_start();
return nonseekable_open(inode, file);/*表示返回的这个设备文件是不可以被seek操作的，nonseekable_open定义在fs.h中*/
}
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) { /*如果没有配置内核CONFIG_WATCHDOG_NOWAYOUT选项,WATCHDOG_NOWAYOUT宏位于include/linux/watchdog.h*/
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;
}
}
/*上面的意思是想要看门狗定时器可以被关闭，则内核不要配置CONFIG_WATCHDOG_NOWAYOUT选项，对于下面这里还要“喂狗”一次，我刚开始觉得不需要，因为在看门狗定时器中断里面不断的在“喂狗”。后来想想，这里还必须要“喂狗”一次，因为当上面我们判断到写入的数据是"V"时，看门狗定时器的当前操作状态马上被设置为关闭，再当驱动去调用看门狗设备驱动的关闭接口函数时，看门狗定时器中断被禁止，无法再实现“喂狗”，所以这里要手动“喂狗”一次，否则定时器溢出系统被复位*/
s3c2410wdt_keepalive();
}
return len;
}
#define OPTIONS (WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE)
/*用于支持看门狗IO控制中获取看门狗信息的命令WDIOC_GETSUPPORT，下面的宏和看门狗信息结构体定义在include/linux/watchdog.h中*/
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;
/*以下对看门狗定时器IO控制的命令定义在watchdog.h中*/
switch (cmd) {
case WDIOC_GETSUPPORT:/*获取看门狗的支持信息，wdt_ident定义在上面*/
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, /*定义为不可定位，即屏蔽seek操作，no_llseek定义在fs.h中*/
.write = s3c2410wdt_write,
.unlocked_ioctl = s3c2410wdt_ioctl,
.open = s3c2410wdt_open,
.release = s3c2410wdt_release,
};
static struct miscdevice s3c2410wdt_miscdev = {
.minor = WATCHDOG_MINOR, //位于include/linux/miscdevic.h中
.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; /*定义一个资源，用来保存获取的watchdog的IO资源*/
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 */
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (res == NULL) {
/*dev_err定义在device.h中，在platform_device.h中已经引用，所以这里就不需再引用*/
dev_err(dev, "no memory resource specified\n");
return -ENOENT;
}
size = (res->end - res->start) + 1;
/*申请watchdog的IO端口资源所占用的IO内存,request_mem_region定义在ioport.h中*/
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;
}
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);
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;
}
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;
}
/*定义在arch/arm/plat-s3c24xx/s3c2410-clock.c中*/
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;
}
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
/*对Watchdog平台设备驱动电源管理的支持。CONFIG_PM这个宏定义在内核中，当配置内核时选上电源管理，则Watchdog平台驱动的设备挂起和恢复功能均有效*/
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 */
/*注意：这是使用了一个__devexit_p，还有前面使用了__devinit和__devexit，我们还是先来讲讲这个：在Linux内核中，使用了大量不同的宏来标记具有不同作用的函数和数据结构，这些宏在include/linux/init.h头文件中定义，编译器通过这些宏可以把代码优化放到合适的内存位置，以减少内存占用和提高内核效率。__devinit、__devexit就是这些宏之一，在probe()和remove()函数中应该使用__devinit和__devexit宏。又当remove()函数使用了__devexit宏时，则在驱动结构体中一定要使用__devexit_p宏来引用remove()，所以下面就用__devexit_p来引用rtc_remove*/
static struct platform_driver s3c2410wdt_driver = {
.probe = s3c2410wdt_probe,
.remove = __devexit_p(s3c2410wdt_remove),
.shutdown = s3c2410wdt_shutdown,
.suspend = s3c2410wdt_suspend,
.resume = s3c2410wdt_resume,
.driver = {
.owner = THIS_MODULE,
.name = "s3c2410-wdt",
/*注意这里的名称一定要和系统中定义平台设备的名称一致，这样才能把平台设备与该平台设备的驱动关联起来*/
},
};
static char banner[] __initdata =
KERN_INFO "S3C2410 Watchdog Timer, (c) 2004 Simtec Electronics\n";
static int __init watchdog_init(void)
{
printk(banner);
return platform_driver_register(&s3c2410wdt_driver);
}
static void __exit watchdog_exit(void)
{
platform_driver_unregister(&s3c2410wdt_driver);
}
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");

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