看門狗是linux驅動的一個重要環節。某些特殊的設備，有時候需要放在一些環境惡劣的地方，比如電信設備。但是，任何軟件都不可能100%沒有bug。如何保證軟件在遇到嚴重bug、死機的時候也能正常運行呢，那么看門狗就是有效的一種方法。看門狗一般要求用戶定時喂狗，如果一段時間沒有喂狗的話，那么系統就會自動重啟。今天，我們就來看看這個看門狗驅動怎么編寫？
1、代碼目錄
drivers/watchdog
2、閱讀目錄下的Kconfig，可以找一個s3c模塊macro
config HAVE_S3C2410_WATCHDOG bool help This will include watchdog timer support for Samsung SoCs. If you want to include watchdog support for any machine, kindly select this in the respective mach-XXXX/Kconfig file. config S3C2410_WATCHDOG tristate "S3C2410 Watchdog" depends on HAVE_S3C2410_WATCHDOG || COMPILE_TEST select WATCHDOG_CORE select MFD_SYSCON if ARCH_EXYNOS help Watchdog timer block in the Samsung SoCs. This will reboot the system when the timer expires with the watchdog enabled. The driver is limited by the speed of the system's PCLK signal, so with reasonably fast systems (PCLK around 50-66MHz) then watchdog intervals of over approximately 20seconds are unavailable. The driver can be built as a module by choosing M, and will be called s3c2410_wdt
3、S3C2410_WATCHDOG主要依賴WATCHDOG_CORE，可以繼續跟蹤Makefile
obj-$(CONFIG_S3C2410_WATCHDOG) += s3c2410_wdt.o
4、macro只依賴一個s3c2410_wdt.c文件，繼續查看
static SIMPLE_DEV_PM_OPS(s3c2410wdt_pm_ops, s3c2410wdt_suspend, s3c2410wdt_resume); static struct platform_driver s3c2410wdt_driver = { .probe = s3c2410wdt_probe, .remove = s3c2410wdt_remove, .shutdown = s3c2410wdt_shutdown, .id_table = s3c2410_wdt_ids, .driver = { .name = "s3c2410-wdt", .pm = &s3c2410wdt_pm_ops, .of_match_table = of_match_ptr(s3c2410_wdt_match), }, }; module_platform_driver(s3c2410wdt_driver); 5、確認driver為platform類型，繼續在probe函數中查找有用的code
ret = watchdog_register_device(&wdt->wdt_device); if (ret) { dev_err(dev, "cannot register watchdog (%d)/n", ret); goto err_cpufreq; } 6、網上繼續查找，尋找到和watchdog有關的數據結構
static const struct watchdog_info s3c2410_wdt_ident = { .options = OPTIONS, .firmware_version = 0, .identity = "S3C2410 Watchdog", }; static const struct watchdog_ops s3c2410wdt_ops = { .owner = THIS_MODULE, .start = s3c2410wdt_start, .stop = s3c2410wdt_stop, .ping = s3c2410wdt_keepalive, .set_timeout = s3c2410wdt_set_heartbeat, .restart = s3c2410wdt_restart, }; static const struct watchdog_device s3c2410_wdd = { .info = &s3c2410_wdt_ident, .ops = &s3c2410wdt_ops, .timeout = S3C2410_WATCHDOG_DEFAULT_TIME, }; 7、找到設備注冊函數、函數結構基本就算結束了，當然有中斷的話，也可以確認一下
ret = devm_request_irq(dev, wdt_irq->start, s3c2410wdt_irq, 0, pdev->name, pdev); if (ret != 0) { dev_err(dev, "failed to install irq (%d)/n", ret); goto err_cpufreq; } 8、有興趣的話，可以找一個函數閱讀一下。比如下面這個重啟函數，可以和spec對比者來看
static int s3c2410wdt_restart(struct watchdog_device *wdd, unsigned long action, void *data) { struct s3c2410_wdt *wdt = watchdog_get_drvdata(wdd); void __iomem *wdt_base = wdt->reg_base; /* disable watchdog, to be safe */ writel(0, wdt_base + S3C2410_WTCON); /* put initial values into count and data */ writel(0x80, wdt_base + S3C2410_WTCNT); writel(0x80, wdt_base + S3C2410_WTDAT); /* set the watchdog to go and reset... */ writel(S3C2410_WTCON_ENABLE | S3C2410_WTCON_DIV16 | S3C2410_WTCON_RSTEN | S3C2410_WTCON_PRESCALE(0x20), wdt_base + S3C2410_WTCON); /* wait for reset to assert... */ mdelay(500); return 0; } 以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持VEVB武林網。
新聞熱點
疑難解答
