linux-kernel - Re: [PATCH] ACPI: video: Invoke

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Date:   Tue, 4 Jul 2023 18:58:53 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Hans de Goede <hdegoede@...hat.com>
Cc:     rafael@...nel.org, lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI: video: Invoke _PS0 at boot for ACPI video

On Tue, Jul 4, 2023 at 9:46 AM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> Screen brightness can only be changed once on some HP laptops.
>
> Vendor identified the root cause as Linux doesn't invoke _PS0 at boot
> for all ACPI devices:

This part of the changelog is confusing, because the evaluation of
_PS0 is not a separate operation.  _PS0 gets evaluated when devices
undergo transitions from low-power states to D0.

>     Scope (\_SB.PC00.GFX0)
>     {
>         Scope (DD1F)
>         {
>             Method (_PS0, 0, Serialized)  // _PS0: Power State 0
>             {
>                 If (CondRefOf (\_SB.PC00.LPCB.EC0.SSBC))
>                 {
>                     \_SB.PC00.LPCB.EC0.SSBC ()
>                 }
>             }
>             ...
>         }
>         ...
>     }
>
> _PS0 doesn't get invoked for all ACPI devices because of commit
> 7cd8407d53ef ("ACPI / PM: Do not execute _PS0 for devices without _PSC
> during initialization").

And yes, Linux doesn't put all of the ACPI devices into D0 during
initialization, but the above commit has a little to do with that.

> For now explicitly call _PS0 for ACPI video to workaround the issue.

This is not what the patch is doing.

> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/acpi/acpi_video.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> index 62f4364e4460..793259bd18c8 100644
> --- a/drivers/acpi/acpi_video.c
> +++ b/drivers/acpi/acpi_video.c
> @@ -2027,6 +2027,8 @@ static int acpi_video_bus_add(struct acpi_device *device)
>         if (error)
>                 goto err_put_video;
>
> +       acpi_device_fix_up_power_extended(device);
> +

I would like to know what Hans thinks about this.

>         pr_info("%s [%s] (multi-head: %s  rom: %s  post: %s)\n",
>                ACPI_VIDEO_DEVICE_NAME, acpi_device_bid(device),
>                video->flags.multihead ? "yes" : "no",
> --