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

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Message-ID: <CAJZ5v0grVpm8MUGYRRhC6VTRRQxvCEmzRJm27F83vJ4a-Wwjhg@mail.gmail.com>
Date: Fri, 16 May 2025 18:56:53 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Armin Wolf <w_armin@....de>
Cc: 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 Fri, May 16, 2025 at 3:59 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Sat, May 3, 2025 at 12:29 AM Armin Wolf <W_Armin@....de> wrote:
> >
> > Am 28.04.25 um 14:34 schrieb Rafael J. Wysocki:
> >
> > > 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.

It just says "This object may exist under a thermal zone or a device"
so I don't see any contradiction.  Section 11.4.13 says where it is
located and Section 11.1.2.1 says when to evaluate it.

However, Section 11.4.13 also says "OSPM will automatically evaluate
_ACx and _PSV objects after executing _SCP" which is not arranged for
in your patch [3/3] IIUC.

Thanks!