watchdog: mt7621: set WDOG_HW_RUNNING bit when appropriate

If the watchdog hardware is enabled/running during boot, e.g.
due to a boot loader configuring it, we must tell the
watchdog framework about this fact so that it can ping the
watchdog until userspace opens the device and takes over
control.

Do so using the WDOG_HW_RUNNING flag that exists for exactly
that use-case.

Given the watchdog driver core doesn't know what timeout was
originally set by whoever started the watchdog (boot loader),
we make sure to update the timeout in the hardware according
to what the watchdog core thinks it is.
Signed-off-by: André Draszik <git@andred.net>
Cc: linux-watchdog@vger.kernel.org
Cc: John Crispin <john@phrozen.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/mt7621_wdt.c

@@ -105,6 +105,11 @@ static int mt7621_wdt_bootcause(void)
 	return 0;
 }
 
+static int mt7621_wdt_is_running(struct watchdog_device *w)
+{
+	return !!(rt_wdt_r32(TIMER_REG_TMR1CTL) & TMR1CTL_ENABLE);
+}
+
 static const struct watchdog_info mt7621_wdt_info = {
 	.identity = "Mediatek Watchdog",
 	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
@@ -144,6 +149,20 @@ static int mt7621_wdt_probe(struct platform_device *pdev)
 	watchdog_init_timeout(&mt7621_wdt_dev, mt7621_wdt_dev.max_timeout,
 			      &pdev->dev);
 	watchdog_set_nowayout(&mt7621_wdt_dev, nowayout);
+	if (mt7621_wdt_is_running(&mt7621_wdt_dev)) {
+		/*
+		 * Make sure to apply timeout from watchdog core, taking
+		 * the prescaler of this driver here into account (the
+		 * boot loader might be using a different prescaler).
+		 *
+		 * To avoid spurious resets because of different scaling,
+		 * we first disable the watchdog, set the new prescaler
+		 * and timeout, and then re-enable the watchdog.
+		 */
+		mt7621_wdt_stop(&mt7621_wdt_dev);
+		mt7621_wdt_start(&mt7621_wdt_dev);
+		set_bit(WDOG_HW_RUNNING, &mt7621_wdt_dev.status);
+	}
 
 	ret = watchdog_register_device(&mt7621_wdt_dev);