[PATCH] hwmon: (gpio-fan) Update the speed cache before dropping the PM reference

[Baek Kyu, Kim]

set_fan_speed() writes the GPIO control value before dropping the runtime
PM reference when stopping the fan. pm_runtime_put_sync() decrements the
usage count even when suspending the device fails, but the error return
currently leaves speed_index at the previous running speed.

A request for that same running speed then returns success without
changing the GPIOs or taking a runtime PM reference. Retrying the stop
instead drops a reference the driver no longer owns and can trigger a
runtime PM usage count underflow warning.

Update speed_index after writing the GPIOs and before dropping the PM
reference. The initial same-speed check already excludes a stopped fan,
so a zero target is sufficient to identify the transition that needs a
PM put. Preserve the PM error return and the CONFIG_PM=n exception.

This keeps the cached control state and PM reference ownership consistent
without restoring running GPIOs after a possibly partial supply failure.
It does not clear persistent runtime PM errors or claim that a failing
regulator has successfully powered off.

Fixes: 0d01110e6356 ("hwmon: (gpio-fan) Add regulator support")

Signed-off-by: Baek Kyu, Kim <pocj8ur4in@xxxxxxxxx>
---
An arm64 QEMU/KVM kernel exercised gpio-fan through hwmon sysfs with
virtual GPIO and regulator providers and the actual runtime PM core.
An injected -EBUSY regulator disable error after a running-to-stopped
request left GPIOs off and PM usage at zero. Before the change the
speed cache stayed running and a repeated stop underflowed PM usage;
after the change the cache stayed stopped and no PM underflow occurred.
No physical fan or RPM was tested.

 drivers/hwmon/gpio-fan.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
index 3f78375eeb448..08b58b49be5b9 100644
--- a/drivers/hwmon/gpio-fan.c
+++ b/drivers/hwmon/gpio-fan.c
@@ -150,7 +150,10 @@ static int set_fan_speed(struct gpio_fan_data *fan_data, int speed_index)
 
 	__set_fan_ctrl(fan_data, fan_data->speed[speed_index].ctrl_val);
 
-	if (fan_data->speed_index > 0 && speed_index == 0) {
+	/* The GPIOs have changed, and a PM put drops the reference on error. */
+	fan_data->speed_index = speed_index;
+
+	if (speed_index == 0) {
 		int ret;
 
 		ret = pm_runtime_put_sync(fan_data->dev);
@@ -158,8 +161,6 @@ static int set_fan_speed(struct gpio_fan_data *fan_data, int speed_index)
 			return ret;
 	}
 
-	fan_data->speed_index = speed_index;
-
 	return 0;
 }
 
-- 
2.55.0