[PATCH] hwmon: (gpd-fan) Reset both fans to automatic on duo boards

[Alexei Solcanu via B4 Relay]

From: Alexei Solcanu <alexei.solcanu@xxxxx>

On boards using gpd_duo_drvdata (GPD Duo, GPD Win 5), writing
pwm1_enable=2 only returns the first fan to EC control. The second fan
keeps its last manual duty cycle, e.g. full speed after pwm1=255, so a
fan control tool that exits leaves it running at that speed.

gpd_duo_write_pwm() writes both fan registers (pwm_write and
pwm_write + 1), but switching to automatic only clears pwm_write.
Also clear pwm_write + 1, so both fans return to EC control.

Tested on a GPD Win 5 (G1618-05). Not tested on the GPD Duo.

Fixes: 0ab88e239439 ("hwmon: add GPD devices sensor driver")
Assisted-by: LLM
Signed-off-by: Alexei Solcanu <alexei.solcanu@xxxxx>
---
Both fans were set to full speed (pwm1_enable=1, pwm1=255), then
switched to automatic (pwm1_enable=2). Values read from the EC 15
seconds later:

                 0x047A  0x047B  fan 1     fan 2
  without patch  0x00    0xf4    2542 rpm  6379 rpm
  with patch     0x00    0x00    2545 rpm  2560 rpm

Fan 2's RPM, found by probing, is at EC 0x0476/0x0477.
---
 drivers/hwmon/gpd-fan.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hwmon/gpd-fan.c b/drivers/hwmon/gpd-fan.c
index ed212615b2f..b3b75f99f58 100644
--- a/drivers/hwmon/gpd-fan.c
+++ b/drivers/hwmon/gpd-fan.c
@@ -444,6 +444,7 @@ static void gpd_duo_set_pwm_enable(struct gpd_fan_data *data, enum FAN_PWM_ENABL
 		break;
 	case AUTOMATIC:
 		gpd_ecram_write(data->drvdata, data->drvdata->pwm_write, 0);
+		gpd_ecram_write(data->drvdata, data->drvdata->pwm_write + 1, 0);
 		break;
 	}
 }

---
base-commit: 3cbb5f15e464583e59c8501a7085ec12b53e23ac
change-id: 20260925-gpd-fan-duo-auto-871de9e006dc

Best regards,
--  
Alexei Solcanu <alexei.solcanu@xxxxx>