linux-kernel - Re: [PATCH v9 7/7] platform/x86: lenovo-wmi-other: Add HWMON for fan reporting/tuning

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Message-Id: <DFOQB6DGBKBZ.39JQKPB7XDSJG@gmail.com>
Date: Wed, 14 Jan 2026 19:16:30 -0500
From: "Kurt Borja" <kuurtb@...il.com>
To: "Rong Zhang" <i@...g.moe>, "Mark Pearson" <mpearson-lenovo@...ebb.ca>,
 "Derek J. Clark" <derekjohn.clark@...il.com>, "Armin Wolf"
 <W_Armin@....de>, "Hans de Goede" <hansg@...nel.org>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: "Guenter Roeck" <linux@...ck-us.net>,
 <platform-driver-x86@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH v9 7/7] platform/x86: lenovo-wmi-other: Add HWMON for
 fan reporting/tuning

Hi Rong,

On Wed Jan 14, 2026 at 7:27 AM -05, Rong Zhang wrote:
> Register an HWMON device for fan reporting/tuning according to
> Capability Data 00 (capdata00) and Fan Test Data (capdata_fan) provided
> by lenovo-wmi-capdata. The corresponding HWMON nodes are:
>
>  - fanX_enable: enable/disable the fan (tunable)
>  - fanX_input: current RPM
>  - fanX_max: maximum RPM
>  - fanX_min: minimum RPM
>  - fanX_target: target RPM (tunable)
>
> Information from capdata00 and capdata_fan are used to control the
> visibility and constraints of HWMON attributes. Fan info from capdata00
> is collected on bind, while fan info from capdata_fan is collected in a
> callback. Once all fan info is collected, register the HWMON device.
>
> Signed-off-by: Rong Zhang <i@...g.moe>
> Reviewed-by: Derek J. Clark <derekjohn.clark@...il.com>
> ---

...

> diff --git a/Documentation/wmi/devices/lenovo-wmi-other.rst b/Documentation/wmi/devices/lenovo-wmi-other.rst
> index 821282e07d93c..bd1d733ff286d 100644
> --- a/Documentation/wmi/devices/lenovo-wmi-other.rst
> +++ b/Documentation/wmi/devices/lenovo-wmi-other.rst
> @@ -31,6 +31,8 @@ under the following path:
>  
>    /sys/class/firmware-attributes/lenovo-wmi-other/attributes/<attribute>/
>  
> +Additionally, this driver also exports attributes to HWMON.
> +
>  LENOVO_CAPABILITY_DATA_00
>  -------------------------
>  
> @@ -39,6 +41,11 @@ WMI GUID ``362A3AFE-3D96-4665-8530-96DAD5BB300E``
>  The LENOVO_CAPABILITY_DATA_00 interface provides various information that
>  does not rely on the gamezone thermal mode.
>  
> +The following HWMON attributes are implemented:
> + - fanX_enable: enable/disable the fan (tunable)

I was testing this series and I'm a bit confused about fanX_enable.

Judging by this comment and also by taking a quick look at the code, it
looks like writting 0 to this attribute disables the fan.

This is however (per hwmon ABI documentation [1]) not how this attribute
should work. IIUC, it is intended for devices which can disable the fan
sensor, not the actual fan.

I fail to see how this feature is useful and I also find it dangerous
for this to be exposed by default, considering the same could be
achieved with the relaxed module parameter, which at least tells the
user to be careful.

Apologies if I missed some previous discussion on this.

[1] https://elixir.bootlin.com/linux/v6.19-rc5/source/Documentation/ABI/testing/sysfs-class-hwmon#L279

-- 
Thanks,
 ~ Kurt