watchdog: Introduce watchdog_stop_on_unregister helper

Many watchdog drivers explicitly stop the watchdog when unregistering it.
While it is unclear if this is actually needed (the whatdog should not be
running at that time if it can be stopped), introduce a helper to
explicitly stop the watchdog in the watchdog core when unregistering it.
This helps reducing driver code size while retaining functionality.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/watchdog/watchdog-kernel-api.txt

@@ -280,6 +280,12 @@ To disable the watchdog on reboot, the user must call the following helper:
 
 static inline void watchdog_stop_on_reboot(struct watchdog_device *wdd);
 
+To disable the watchdog when unregistering the watchdog, the user must call
+the following helper. Note that this will only stop the watchdog if the
+nowayout flag is not set.
+
+static inline void watchdog_stop_on_unregister(struct watchdog_device *wdd);
+
 To change the priority of the restart handler the following helper should be
 used:
 

drivers/watchdog/watchdog_dev.c

@@ -987,6 +987,11 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
 	wdd->wd_data = NULL;
 	mutex_unlock(&wd_data->lock);
 
+	if (watchdog_active(wdd) &&
+	    test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
+		watchdog_stop(wdd);
+	}
+
 	cancel_delayed_work_sync(&wd_data->work);
 
 	kref_put(&wd_data->kref, watchdog_core_data_release);

include/linux/watchdog.h

@@ -117,6 +117,7 @@ struct watchdog_device {
 #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;
 };
 
@@ -151,6 +152,12 @@ static inline void watchdog_stop_on_reboot(struct watchdog_device *wdd)
 	set_bit(WDOG_STOP_ON_REBOOT, &wdd->status);
 }
 
+/* Use the following function to stop the watchdog when unregistering it */
+static inline void watchdog_stop_on_unregister(struct watchdog_device *wdd)
+{
+	set_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status);
+}
+
 /* Use the following function to check if a timeout value is invalid */
 static inline bool watchdog_timeout_invalid(struct watchdog_device *wdd, unsigned int t)
 {