linux-kernel - Re: [PATCH v2 0/6] ACPI fan

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Message-ID: <de8dc59e-d301-4954-b39c-f032b6aa0db9@gmx.de>
Date: Thu, 23 Oct 2025 22:13:35 +0200
From: Armin Wolf <W_Armin@....de>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: lenb@...nel.org, linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] ACPI fan _DSM support

Am 23.10.25 um 21:22 schrieb Rafael J. Wysocki:

> On Thu, Oct 23, 2025 at 11:59 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Wed, Oct 22, 2025 at 11:41 PM Armin Wolf <W_Armin@....de> wrote:
>>> Am 08.10.25 um 01:41 schrieb Armin Wolf:
>>>
>>>> Microsoft has designed a _DSM interface for the ACPI fan device [1]
>>>> that allows the OS to set fan speed trip points. The ACPI firmware
>>>> will notify the ACPI fan device when said trip points are triggered.
>>>>
>>>> Unfortunately some device manufacturers (like HP) blindly assume that
>>>> the OS will use this _DSM interface and thus only update the fan speed
>>>> value returned by the _FST control method when sending a notification
>>>> to the ACPI fan device. This results in stale fan speed values being
>>>> reported by the ACPI fan driver [2].
>>>>
>>>> The first patch performs a simple cleanup in order to reduce the usage
>>>> of the acpi_device struct. The second patch fixes an issue with some
>>>> 64-bit ACPI implementations where an invalid value was reported
>>>> instead of the standard ACPI placeholder value (0xFFFFFFFF). The third
>>>> patch fixes an unrelated issue inside the hwmon support code while the
>>>> next two patches add support for the ACPI fan notifications as
>>>> specified in ACPI 11.2.3. The last patch finally adds support for the
>>>> Microsoft _DSM interface.
>>>>
>>>> All patches where tested with a custom SSDT [3] and the acpi_call [4]
>>>> kernel module and appear to work just fine.
>>> Any thought on this?
>> Not yet, but I'm going to get to it today.
>>
>>> I tested it with a custom SSDT, so i can prove that those patches work.
>> OK
> I've applied two first patches for 6.19 and the third one for 6.18-rc, as a fix.

Please note that the third patch depends on the first patch! Otherwise you will
get a runtime error when acpi_fan_hwmon_read() tries to cast the platform device
to a ACPI device.

> My understanding is that patches [4-5/6] are preparations for the last
> one that needs a pointer to the MSFT documentation it is based on.

I understand, i will send a v3 series without the first three patch and this
issue being addressed.

Thanks,
Armin Wolf