Linux驱动开发—看门狗（watchdog）设备框架

一、看门狗设备驱动框架简介

看门狗框架涉及drivers/watchdog/watchdog_dev.c 、drivers/watchdog/watchdog_core.c、drivers/watchdog/watchdog_pretimeout.c 这三个源文件，其本质是misc设备。

• watchdog_dev.c：作为上层，注册字符设备操作函数集file_operations结构体变量，与应用层对接。
• watchdog_core.c：作为看门狗驱动框架核心层，提供看门狗设备的注册、卸载等相关API函数。
• watchdog_pretimeout.c：主要涉及看门狗定时、预超时相关处理。

二、struct watchdog_device结构体（描述看门狗设备）

struct watchdog_device {
	int id;
	struct device *parent;
	const struct attribute_group **groups;
	const struct watchdog_info *info;
	const struct watchdog_ops *ops;
	const struct watchdog_governor *gov;
	unsigned int bootstatus;
	unsigned int timeout;
	unsigned int pretimeout;
	unsigned int min_timeout;
	unsigned int max_timeout;
	unsigned int min_hw_heartbeat_ms;
	unsigned int max_hw_heartbeat_ms;
	struct notifier_block reboot_nb;
	struct notifier_block restart_nb;
	void *driver_data;
	struct watchdog_core_data *wd_data;
	unsigned long status;
/* Bit numbers for status flags */
#define WDOG_ACTIVE		0	/* Is the watchdog running/active */
#define WDOG_NO_WAY_OUT		1	/* Is 'nowayout' feature set ? */
#define WDOG_STOP_ON_REBOOT	2	/* Should be stopped on reboot */
#define WDOG_HW_RUNNING		3	/* True if HW watchdog running */
#define WDOG_STOP_ON_UNREGISTER	4	/* Should be stopped on unregister */
	struct list_head deferred;
};

• id：id号，有watchdog_register_device函数注册时自动分配。
• parent：父设备，可填充&p