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hwmon: mlxreg-fan: Prevent fans from getting stuck at 0 RPM

PATCH Applied Vadim Pasternak 2 participants 2 messages Jul 30, 2025 – Jul 31, 2025 Hardware monitoring

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Vadim Pasternak

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PATCH 1/1 hwmon: mlxreg-fan: Prevent fans from getting stuck at 0 RPM

The fans controlled by the driver can get stuck at 0 RPM if they are configured below a 20% duty cycle. The driver tries to avoid this by enforcing a minimum duty cycle of 20%, but this is done after the fans are registered with the thermal subsystem. This is too late as the thermal subsystem can set their current state before the driver is able to enforce the minimum duty cycle.

Fix by setting the minimum duty cycle before registering the fans with the thermal subsystem.

Fixes d7efb2ebc7b3 ("hwmon: (mlxreg-fan) Extend driver to support multiply cooling devices")
Reported-by Nikolay Aleksandrov <[email protected]>
Tested-by Nikolay Aleksandrov <[email protected]>
Signed-off-by Ido Schimmel <[email protected]>
Signed-off-by Vadim Pasternak <[email protected]>
---
 drivers/hwmon/mlxreg-fan.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
drivers/hwmon/mlxreg-fan.c +2 -3
index 01faf1a8f55a..137a90dd2075 100644
@@ -581,15 +581,14 @@ static int mlxreg_fan_cooling_config(struct device *dev, struct mlxreg_fan *fan)
 		if (!pwm->connected)
 			continue;
 		pwm->fan = fan;
+		/* Set minimal PWM speed. */
+		pwm->last_hwmon_state = MLXREG_FAN_PWM_DUTY2STATE(MLXREG_FAN_MIN_DUTY);
 		pwm->cdev = devm_thermal_of_cooling_device_register(dev, NULL, mlxreg_fan_name[i],
 								    pwm, &mlxreg_fan_cooling_ops);
 		if (IS_ERR(pwm->cdev)) {
 			dev_err(dev, "Failed to register cooling device\n");
 			return PTR_ERR(pwm->cdev);
 		}
-
-		/* Set minimal PWM speed. */
-		pwm->last_hwmon_state = MLXREG_FAN_PWM_DUTY2STATE(MLXREG_FAN_MIN_DUTY);
 	}
 
 	return 0;
Signature · 1 line
2.34.1
maintainer Applied
#1 lore raw
Quoted 7 lines · Vadim Pasternak

The fans controlled by the driver can get stuck at 0 RPM if they are configured below a 20% duty cycle. The driver tries to avoid this by enforcing a minimum duty cycle of 20%, but this is done after the fans are registered with the thermal subsystem. This is too late as the thermal subsystem can set their current state before the driver is able to enforce the minimum duty cycle.

Quoted 8 lines

Fix by setting the minimum duty cycle before registering the fans with the thermal subsystem.

Fixes d7efb2ebc7b3 ("hwmon: (mlxreg-fan) Extend driver to support multiply cooling devices")
Reported-by Nikolay Aleksandrov <[email protected]>
Tested-by Nikolay Aleksandrov <[email protected]>
Signed-off-by Ido Schimmel <[email protected]>
Signed-off-by Vadim Pasternak <[email protected]>

Applied.

Guenter