On Tue, Jul 4, 2023 at 9:46 AM Kai-Heng Feng
<kai.heng.feng@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> ---
> 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",
> --
