[PATCH v2] hwmon: (gpio-fan) fix pm_runtime imbalance for alarm-only fans

[Cong Nguyen <congnt264@gmail.com>]

pm_runtime_enable() runs unconditionally in probe, but the devm cleanup
that calls pm_runtime_disable() is only registered when control GPIOs
are present. Alarm-only fans never get it, so unbind warns about the
missing disable.

Switch to devm_pm_runtime_enable(), registered before gpio_fan_stop()'s
devm action so LIFO teardown runs gpio_fan_stop() first. gpio_fan_stop()
calls set_fan_speed(0) -> pm_runtime_put_sync(), which needs PM still
enabled to reach gpio_fan_runtime_suspend() and turn the regulator off;
registering enable after gpio_fan_stop() (as v1 did) reverses that order
and leaves the regulator on.

Fixes: 0d01110e6356 ("hwmon: (gpio-fan) Add regulator support")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/b9792be3-fcd6-468c-9149-7e33640ee167@roeck-us.net
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4
Signed-off-by: Cong Nguyen <congnt264@gmail.com>
---
Changes in v2:
- v1's devm_pm_runtime_enable() was registered after gpio_fan_stop()'s
  devm action, reversing LIFO teardown order and leaving the regulator
  enabled on unbind (Guenter/Sashiko). Moved it earlier so gpio_fan_stop()
  registers first.

 drivers/hwmon/gpio-fan.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
index 084828e1e281..988f52d11ce2 100644
--- a/drivers/hwmon/gpio-fan.c
+++ b/drivers/hwmon/gpio-fan.c
@@ -524,8 +524,6 @@ static void gpio_fan_stop(void *data)
 	mutex_lock(&fan_data->lock);
 	set_fan_speed(data, 0);
 	mutex_unlock(&fan_data->lock);
-
-	pm_runtime_disable(fan_data->dev);
 }
 
 static int gpio_fan_probe(struct platform_device *pdev)
@@ -553,6 +551,16 @@ static int gpio_fan_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(fan_data->supply),
 				     "Failed to get fan-supply");
 
+	/*
+	 * Register before gpio_fan_stop()'s devm action: LIFO teardown must
+	 * run gpio_fan_stop() (needs PM enabled to disable the regulator)
+	 * before this disables PM.
+	 */
+	pm_runtime_set_suspended(&pdev->dev);
+	err = devm_pm_runtime_enable(&pdev->dev);
+	if (err)
+		return err;
+
 	/* Configure control GPIOs if available. */
 	if (fan_data->gpios && fan_data->num_gpios > 0) {
 		if (!fan_data->speed || fan_data->num_speed <= 1)
@@ -580,8 +588,6 @@ static int gpio_fan_probe(struct platform_device *pdev)
 			return err;
 	}
 
-	pm_runtime_set_suspended(&pdev->dev);
-	pm_runtime_enable(&pdev->dev);
 	/* If current GPIO state is active, mark RPM as active as well */
 	if (fan_data->speed_index > 0) {
 		int ret;
-- 
2.25.1