watchdog: Make stop function optional

Not all hardware watchdogs can be stopped. The driver for
such watchdogs would typically only set the WATCHDOG_HW_RUNNING
flag in its stop function. Make the stop function optional and set
WATCHDOG_HW_RUNNING in the watchdog core if it is not provided.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/watchdog_core.c

@@ -199,7 +199,7 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
 		return -EINVAL;
 
 	/* Mandatory operations need to be supported */
-	if (wdd->ops->start == NULL || wdd->ops->stop == NULL)
+	if (!wdd->ops->start || (!wdd->ops->stop && !wdd->max_hw_heartbeat_ms))
 		return -EINVAL;
 
 	watchdog_check_min_max_timeout(wdd);

drivers/watchdog/watchdog_dev.c

@@ -246,7 +246,11 @@ static int watchdog_stop(struct watchdog_device *wdd)
 		return -EBUSY;
 	}
 
-	err = wdd->ops->stop(wdd);
+	if (wdd->ops->stop)
+		err = wdd->ops->stop(wdd);
+	else
+		set_bit(WDOG_HW_RUNNING, &wdd->status);
+
 	if (err == 0) {
 		clear_bit(WDOG_ACTIVE, &wdd->status);
 		watchdog_update_worker(wdd);