[PATCH] watchdog: mtk_wdt: Stop a running watchdog over system sleep even if not opened

[zoan37 <agentzoan@gmail.com>]

mtk_wdt_suspend() and mtk_wdt_resume() only stop and restart the
watchdog when it is active, that is, when userspace has opened it.

But a watchdog that the bootloader left enabled stays enabled at probe,
marked WDOG_HW_RUNNING, and the watchdog core pings it until userspace
takes over; that has been the case since
commit bbece05c0d3a ("watchdog: mtk_wdt: Remove mtk_wdt_stop() in probe()
to prevent the system freeze and it doesn't reboot by watchdog problem").
If the system suspends before userspace opens the device, or userspace
never does, nothing stops the watchdog and nothing pings it while the
system sleeps, so it resets the system one timeout (31 s by default)
into the sleep.

Also stop it on suspend and restart it on resume when it is running in
hardware, like sp805_wdt does.

Fixes: bbece05c0d3a ("watchdog: mtk_wdt: Remove mtk_wdt_stop() in probe() to prevent the system freeze and it doesn't reboot by watchdog problem")
Assisted-by: LLM
Signed-off-by: zoan37 <agentzoan@gmail.com>
---

Notes:
    Testing: on an MT8189 Chromebook (next-20261008 plus MT8189 support)
    whose firmware leaves the watchdog off; a local module parameter starts
    it in probe the same way a bootloader-enabled watchdog is picked up
    (WDOG_HW_RUNNING set, fed by the watchdog core, nobody opening
    /dev/watchdog). Without this patch the board reset about 30 s into
    s2idle; with it a 10-minute s2idle sleep came back without a reset.
    Not tested with a watchdog actually left enabled by a bootloader.
    Compile-tested (W=1) on next-20261008.

 drivers/watchdog/mtk_wdt.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/mtk_wdt.c b/drivers/watchdog/mtk_wdt.c
index 1630ab65d593..ff72e0fb1154 100644
--- a/drivers/watchdog/mtk_wdt.c
+++ b/drivers/watchdog/mtk_wdt.c
@@ -572,7 +572,8 @@ static int mtk_wdt_suspend(struct device *dev)
 {
 	struct mtk_wdt_dev *mtk_wdt = dev_get_drvdata(dev);
 
-	if (watchdog_active(&mtk_wdt->wdt_dev))
+	if (watchdog_active(&mtk_wdt->wdt_dev) ||
+	    watchdog_hw_running(&mtk_wdt->wdt_dev))
 		mtk_wdt_stop(&mtk_wdt->wdt_dev);
 
 	return 0;
@@ -582,7 +583,8 @@ static int mtk_wdt_resume(struct device *dev)
 {
 	struct mtk_wdt_dev *mtk_wdt = dev_get_drvdata(dev);
 
-	if (watchdog_active(&mtk_wdt->wdt_dev)) {
+	if (watchdog_active(&mtk_wdt->wdt_dev) ||
+	    watchdog_hw_running(&mtk_wdt->wdt_dev)) {
 		mtk_wdt_start(&mtk_wdt->wdt_dev);
 		mtk_wdt_ping(&mtk_wdt->wdt_dev);
 	}

base-commit: aac26bee2287c88af5be5a5ff96d783b19a28790
-- 
2.43.0