On Wed, Jul 5, 2023 at 12:59 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>
> 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.
But not at boot.
>
> > 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.
Devices without _PSC now doesn't have _PS0 evaluated at boot time. I
don't quite understand why it's not related to this commit?
>
> > For now explicitly call _PS0 for ACPI video to workaround the issue.
>
> This is not what the patch is doing.
To be specific, it's for the child device nodes under ACPI GFX.
Kai-Heng
>
> > 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",
> > --
