linux-kernel - Re: [PATCH 0/3] ACPI: thermal: Properly support the

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Message-ID: <CAJZ5v0icUnepOwb87k44nAt1ZwfHp_BqSBzS-TrQWJ_4E3Ls=g@mail.gmail.com>
Date: Mon, 28 Apr 2025 14:34:12 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Armin Wolf <W_Armin@....de>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, rui.zhang@...el.com, lenb@...nel.org, 
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] ACPI: thermal: Properly support the _SCP control method

On Mon, Apr 28, 2025 at 2:31 PM Armin Wolf <W_Armin@....de> wrote:
>
> Am 27.04.25 um 00:52 schrieb Armin Wolf:
>
> > Am 26.04.25 um 15:12 schrieb Rafael J. Wysocki:
> >
> >> On Sat, Apr 26, 2025 at 1:20 AM Armin Wolf <W_Armin@....de> wrote:
> >>> Am 10.04.25 um 18:54 schrieb Armin Wolf:
> >>>
> >>>> The ACPI specification defines an interface for the operating system
> >>>> to change the preferred cooling mode of a given ACPI thermal zone.
> >>>> This interface takes the form of a special ACPI control method called
> >>>> _SCP (see section 11.4.13 for details) and is already supported by the
> >>>> ACPI thermal driver.
> >>>>
> >>>> However this support as many issues:
> >>>>
> >>>>    - the kernel advertises support for the "3.0 _SCP Extensions"
> >>>> yet the
> >>>>      ACPI thermal driver does not support those extensions. This may
> >>>>      confuse the ACPI firmware.
> >>>>
> >>>>    - the execution of the _SCP control method happens after the driver
> >>>>      retrieved the trip point values. This conflicts with the ACPI
> >>>>      specification:
> >>>>
> >>>>        "OSPM will automatically evaluate _ACx and _PSV objects after
> >>>>         executing _SCP."
> >>>>
> >>>>    - the cooling mode is hardcoded to active cooling and cannot be
> >>>>      changed by the user.
> >>>>
> >>>> Those issues are fixed in this patch series. In the end the user
> >>>> will be able to tell the ACPI firmware wether he prefers active or
> >>>> passive cooling. This setting will also be interesting for
> >>>> applications like TLP (https://linrunner.de/tlp/index.html).
> >>>>
> >>>> The whole series was tested on various devices supporting the _SCP
> >>>> control method and on a device without the _SCP control method and
> >>>> appears to work flawlessly.
> >>> Any updates on this? I can proof that the new interface for setting
> >>> the cooling mode
> >>> works. Additionally the first two patches fix two issues inside the
> >>> underlying code
> >>> itself, so having them inside the mainline tree would be beneficial
> >>> to users.
> >> Sure.
> >>
> >> I'm going to get to them next week, probably on Monday.
> >
> > Ok, thanks.
> >
> > Armin Wolf
> >
> I am a bit ashamed of myself but i think we need to put this patch series on hold after all :(.
>
> The reason of this is that i am confused by the ACPI specification regarding _SCP:
>
>         11.1.2.1. OSPM Change of Cooling Policy
>
>         When OSPM changes the platform’s cooling policy from one cooling mode to the other, the following occurs:
>
>         1. OSPM notifies the platform of the new cooling mode by running the Set Cooling Policy (_SCP) control method in all thermal zones and invoking the OS-specific Set Cooling Policy interface to all participating devices in each thermal zone.
>
>         2. Thresholds are updated in the hardware and OSPM is notified of the change.
>
>         3. OSPM re-evaluates the active and passive cooling temperature trip points for the zone and all devices in the zone to obtain the new temperature thresholds.
>
> This section of the ACPI specification tells me that we need to evaluate the _SCP control method of all ACPI thermal zones
> at the same time, yet section 11.4.13. tells me that each _SCP control methods belongs to the individual thermal zone.
>
> The reason why i am concerned by this is because Windows adheres to section 11.1.2.1. and only exposes this setting
> as a global tunable. This might cause device manufacturers to depend on this behavior and lead to strange things
> should two thermal zones have different _SCP settings.
>
> I will ask the UEFI mailing list which behavior is expected by the ACPI specification. Until then i suggest that
> we put this patch series on hold.

Sure, no problem.

Please resend it when you think it is good to go.

Thanks!