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

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Message-ID: <CAJZ5v0idydJCQqnEs38KJT+1TmVJuhLeCFikypDLD1Yd_8zWhg@mail.gmail.com>
Date: Thu, 23 Oct 2025 21:22:38 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Armin Wolf <w_armin@....de>
Cc: lenb@...nel.org, linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] ACPI fan _DSM support

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.

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.