Re: [PATCH 0/3] ACPI: thermal: Properly support the _SCP control method

[Armin Wolf]

Am 16.05.25 um 18:56 schrieb Rafael J. Wysocki:

> On Fri, May 16, 2025 at 3:59 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > On Sat, May 3, 2025 at 12:29 AM Armin Wolf <W_Armin@xxxxxx> 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@xxxxxx> 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@xxxxxx> 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!

This is incorrect, i do call acpi_thermal_trips_update() after setting _SCP in cooling_mode_store().

Thanks,
Armin Wolf