linux-kernel - Re: [PATCH v3] ACPI: video: Put ACPI video and its child devices to D0 at boot

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Date:   Fri, 21 Jul 2023 17:45:53 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>, hdegoede@...hat.com
Cc:     rafael@...nel.org, lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ACPI: video: Put ACPI video and its child devices to
 D0 at boot

Thanks for the update!

On Fri, Jul 21, 2023 at 5:22 PM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> Screen brightness can only be changed once on HP ZBook Fury 16 G10.
>
> Vendor identified the root cause as Linux doesn't invoke _PS0 at boot
> for all ACPI devices:
>
>     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 ()
>                 }
>             }
>             ...
>         }
>         ...
>     }
>
> The \_SB.PC00.GFX0.DD1F is the panel device, and its _PS0 needs to be
> executed to make the brightness control work properly.
>
> _PS0 doesn't get invoked for this device because _PSC is missing,
> which violates ACPI spec 6.3, section 7.3.6. Commit 7cd8407d53ef
> ("ACPI / PM: Do not execute _PS0 for devices without _PSC during
> initialization") tried to workaround missing _PSC on defective
> firmwares, but got reverted because of regression.
>
> So the safest approach is to use acpi_device_fix_up_power_extended() to
> put ACPI video and its child devices to D0 to workaround the issue.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217683
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>

Hans, what do you think?

> ---
> v3:
>  - Wording change to make it clear it's a firmware issue.
>  - Specify the device name in comment.
>
> v2:
>  - Wording
>  - Bugzilla
>  - Add comment
>
>  drivers/acpi/acpi_video.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> index 62f4364e4460..1732780a672b 100644
> --- a/drivers/acpi/acpi_video.c
> +++ b/drivers/acpi/acpi_video.c
> @@ -2027,6 +2027,12 @@ static int acpi_video_bus_add(struct acpi_device *device)
>         if (error)
>                 goto err_put_video;
>
> +       /*
> +        * HP ZBook Fury 16 G10 requires ACPI video's child devices have _PS0
> +        * evaluated to have functional panel brightness control.
> +        */
> +       acpi_device_fix_up_power_extended(device);
> +
>         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",
> --
> 2.34.1
>