Thanks for the update!
On Fri, Jul 21, 2023 at 5:22 PM Kai-Heng Feng
<kai.heng.feng@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
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
>
