Re: [PATCH] platform/x86: hp-wmi: Disable hwmon attributes when no fans are usable

[Ilpo Järvinen]

On Sat, 17 Oct 2026, Krishna Chomal wrote:

> Currently, hp_wmi_hwmon_is_visible() checks whether fan RPM queries
> succeed before exposing fan1_input and fan2_input, but pwm1_enable
> remains visible always, even when fan support is unavailable. 

Why does it yield different result from is_visible?

...Somehow I find starting with this more confusing than helpful.

> On some
> devices, such as certain Omnibook models, the firmware does not provide
> functional WMI fan methods. Exposing pwm1_enable on these devices can
> mislead userspace and cause fan mode changes to fail.
> 
> Additionally, some firmware implementations provide stub methods
> that return an all-zero buffer instead of an error. In this case,
> hp_wmi_get_active_fan_speed() and hp_wmi_get_fan_speed() can report 0
> RPM even when the fan is physically spinning.
> 
> Use the result of fan count query (fetched from firmware once in
> hp_wmi_setup_fan_settings(), and cached in hwmon private data) to
> determine whether fan related attributes should be exposed.
> 
> The fan count query can have the following outcomes:
> * Negative: The WMI query failed. Other fan-related queries are also
>   expected to fail, so disable fan support.
> * Zero (stub firmware): The methods return zero-filled responses without
>   providing functional fan support, so disable fan support.
> * Zero (genuine firmware): No fans are exposed through WMI, so disable
>   fan support.
> * Positive (1 or 2): Firmware reports one or more fans, so allow fan
>   support. Per-channel RPM queries continue to determine which
>   individual fan input attributes are exposed.
> 
> When fan support is unavailable, hide the fan and PWM attributes and
> skip applying the initial fan settings.
> 
> Tested on: HP OmniBook 5 Laptop 16-ag1xxx (board: 8DF4)
> 
> Tested-by: Lorenzo Collevecchio <lorenzocollevecchio17@xxxxxxxxx>
> Reported-by: Lorenzo Collevecchio <lorenzocollevecchio17@xxxxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=222138
> Signed-off-by: Krishna Chomal <krishna.chomal108@xxxxxxxxx>
> ---
>  drivers/platform/x86/hp/hp-wmi.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/platform/x86/hp/hp-wmi.c b/drivers/platform/x86/hp/hp-wmi.c
> index 0eac5e1d9cdb..52077833ac89 100644
> --- a/drivers/platform/x86/hp/hp-wmi.c
> +++ b/drivers/platform/x86/hp/hp-wmi.c
> @@ -651,6 +651,7 @@ enum pwm_modes {
>  
>  struct hp_wmi_hwmon_priv {
>  	struct mutex lock;	/* protects mode, pwm */
> +	int fan_count;
>  	u8 min_rpm;
>  	u8 max_rpm;
>  	u8 mode;
> @@ -2950,12 +2951,18 @@ static umode_t hp_wmi_hwmon_is_visible(const void *data,
>  				       enum hwmon_sensor_types type,
>  				       u32 attr, int channel)
>  {
> +	const struct hp_wmi_hwmon_priv *priv = data;
> +
>  	switch (type) {
>  	case hwmon_pwm:
> +		if (priv->fan_count <= 0)
> +			return 0;
>  		if (attr == hwmon_pwm_input && !hp_wmi_fan_control_supported())
>  			return 0;
>  		return 0644;
>  	case hwmon_fan:
> +		if (priv->fan_count <= 0)
> +			return 0;
>  		if (hp_wmi_fan_control_supported()) {
>  			if (hp_wmi_get_active_fan_speed(channel) >= 0)
>  				return 0444;
> @@ -3124,6 +3131,7 @@ static int hp_wmi_setup_fan_settings(struct hp_wmi_hwmon_priv *priv)
>  
>  	/* Default behaviour on hwmon init is automatic mode */
>  	priv->mode = PWM_MODE_AUTO;
> +	priv->fan_count = hp_wmi_get_fan_count_userdefine_trigger();
>  
>  	/* Bypass devices without fan control support. */
>  	if (!hp_wmi_fan_table_supported())
> @@ -3208,6 +3216,11 @@ static int hp_wmi_hwmon_init(void)
>  		return PTR_ERR(hwmon);
>  	}
>  
> +	if (priv->fan_count <= 0) {
> +		dev_info(dev, "No usable fans reported by WMI, disabling fan support\n");
> +		return 0;
> +	}
> +
>  	ret = hp_wmi_apply_fan_settings(priv);
>  	if (ret)
>  		dev_warn(dev, "Failed to apply initial fan settings: %d\n", ret);
> 

-- 
 i.