[PATCH v2 5/6] watchdog: starfive: avoid PM refcount underflow in shutdown

[William Theesfeld]

starfive_wdt_shutdown() unconditionally calls starfive_wdt_pm_stop(),
which drops a runtime PM reference via pm_runtime_put_sync().  If the
device was never opened (so there was no matching pm_start()), and
early_enable is also off (so probe already balanced its own get/put),
the counter is at zero and put_sync() drives it negative.

Only call pm_stop() when WDOG_ACTIVE is set (meaning a paired
pm_start() happened on open).  For the early_enable-and-never-opened
case, the framework state is WDOG_HW_RUNNING without WDOG_ACTIVE; in
that case stop just the hardware so the watchdog does not keep
ticking through shutdown, while leaving the PM refcount for the
remove path to release.

Signed-off-by: William Theesfeld <william@xxxxxxxxxxxxx>
---
 drivers/watchdog/starfive-wdt.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/starfive-wdt.c b/drivers/watchdog/starfive-wdt.c
index 4926984bf..848935dc6 100644
--- a/drivers/watchdog/starfive-wdt.c
+++ b/drivers/watchdog/starfive-wdt.c
@@ -549,7 +549,19 @@ static void starfive_wdt_shutdown(struct platform_device *pdev)
 {
 	struct starfive_wdt *wdt = platform_get_drvdata(pdev);
 
-	starfive_wdt_pm_stop(&wdt->wdd);
+	/*
+	 * Only drop a runtime PM reference when we actually hold one.  The
+	 * watchdog framework increments it via pm_start() on open; when
+	 * early_enable started the hardware without an open, the reference
+	 * was taken at probe time and the framework state reads as
+	 * WDOG_HW_RUNNING without WDOG_ACTIVE.  In the inactive-and-not-
+	 * running case there is nothing for us to do and dropping the
+	 * counter unconditionally would underflow it.
+	 */
+	if (watchdog_active(&wdt->wdd))
+		starfive_wdt_pm_stop(&wdt->wdd);
+	else if (test_bit(WDOG_HW_RUNNING, &wdt->wdd.status))
+		starfive_wdt_stop(wdt);
 }
 
 static int starfive_wdt_suspend(struct device *dev)
-- 
2.54.0