watchdog: dw_wdt: add stop watchdog operation

The only way of stopping the watchdog is by resetting it.
Add the watchdog op for stopping the device and reset if
a reset line is provided.

At same time WDOG_HW_RUNNING should be remove from dw_wdt_start.
As commented by Guenter Roeck:
dw_wdt sets WDOG_HW_RUNNING in its open function. Result is
that the kref_get() in watchdog_open() won't be executed. But then
kref_put() in close will be called since the watchdog now does stop.
This causes the imbalance.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: linux-watchdog@vger.kernel.org
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/dw_wdt.c

@@ -127,14 +127,27 @@ static int dw_wdt_start(struct watchdog_device *wdd)
 
 	dw_wdt_set_timeout(wdd, wdd->timeout);
 
-	set_bit(WDOG_HW_RUNNING, &wdd->status);
-
 	writel(WDOG_CONTROL_REG_WDT_EN_MASK,
 	       dw_wdt->regs + WDOG_CONTROL_REG_OFFSET);
 
 	return 0;
 }
 
+static int dw_wdt_stop(struct watchdog_device *wdd)
+{
+	struct dw_wdt *dw_wdt = to_dw_wdt(wdd);
+
+	if (!dw_wdt->rst) {
+		set_bit(WDOG_HW_RUNNING, &wdd->status);
+		return 0;
+	}
+
+	reset_control_assert(dw_wdt->rst);
+	reset_control_deassert(dw_wdt->rst);
+
+	return 0;
+}
+
 static int dw_wdt_restart(struct watchdog_device *wdd,
 			  unsigned long action, void *data)
 {
@@ -173,6 +186,7 @@ static const struct watchdog_info dw_wdt_ident = {
 static const struct watchdog_ops dw_wdt_ops = {
 	.owner		= THIS_MODULE,
 	.start		= dw_wdt_start,
+	.stop		= dw_wdt_stop,
 	.ping		= dw_wdt_ping,
 	.set_timeout	= dw_wdt_set_timeout,
 	.get_timeleft	= dw_wdt_get_timeleft,