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:
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 all ACPI devices because of commit
7cd8407d53ef ("ACPI / PM: Do not execute _PS0 for devices without _PSC
during initialization"). For now 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 <[email protected]>
---
v2:
- Wording
- Bugzilla
- Add comment
drivers/acpi/acpi_video.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 62f4364e4460..bac614e9fe56 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -2027,6 +2027,13 @@ static int acpi_video_bus_add(struct acpi_device *device)
if (error)
goto err_put_video;
+
+ /*
+ * Some HP laptops require 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
On Wed, Jul 19, 2023 at 4:33 AM Kai-Heng Feng
<[email protected]> 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:
No, it doesn't and it won't. For the reason why please see the
comment in acpi_bus_init_power().
BTW, missing _PSC for a device that has _PS0 violates Section 7.3.6.
_PSC (Power State Current) of the ACPI specification, so this is a
platform firmware problem.
> 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 all ACPI devices because of commit
> 7cd8407d53ef ("ACPI / PM: Do not execute _PS0 for devices without _PSC
> during initialization"). For now use acpi_device_fix_up_power_extended()
> to put ACPI video and its child devices to D0 to workaround the issue.
The above paragraph is misleading the reader into thinking that the
issue was introduced by a kernel change while the issue really is
there in the platform firmware and it is the missing _PSC.
Blaming kernel changes for platform firmware defects is not really productive.
So this really is a workaround for defective platform firmware on the
affected systems and it should be documented as such.
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217683
> Signed-off-by: Kai-Heng Feng <[email protected]>
> ---
> v2:
> - Wording
> - Bugzilla
> - Add comment
>
> drivers/acpi/acpi_video.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> index 62f4364e4460..bac614e9fe56 100644
> --- a/drivers/acpi/acpi_video.c
> +++ b/drivers/acpi/acpi_video.c
> @@ -2027,6 +2027,13 @@ static int acpi_video_bus_add(struct acpi_device *device)
> if (error)
> goto err_put_video;
>
> +
> + /*
> + * Some HP laptops require ACPI video's child devices have _PS0
> + * evaluated to have functional panel brightness control.
So the comment should mention the platform firmware defect and it
shouldn't say "some" but explicitly identify the defective platforms.
> + */
> + acpi_device_fix_up_power_extended(device);
> +
And the code change itself is simple enough, so it can be made as long
as it is fine with Hans.
> 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",
> --
On Fri, Jul 21, 2023 at 1:32 AM Rafael J. Wysocki <[email protected]> wrote:
>
> On Wed, Jul 19, 2023 at 4:33 AM Kai-Heng Feng
> <[email protected]> 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:
>
> No, it doesn't and it won't. For the reason why please see the
> comment in acpi_bus_init_power().
Understood.
>
> BTW, missing _PSC for a device that has _PS0 violates Section 7.3.6.
> _PSC (Power State Current) of the ACPI specification, so this is a
> platform firmware problem.
This means most if not all platforms have this problem.
>
> > 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 all ACPI devices because of commit
> > 7cd8407d53ef ("ACPI / PM: Do not execute _PS0 for devices without _PSC
> > during initialization"). For now use acpi_device_fix_up_power_extended()
> > to put ACPI video and its child devices to D0 to workaround the issue.
>
> The above paragraph is misleading the reader into thinking that the
> issue was introduced by a kernel change while the issue really is
> there in the platform firmware and it is the missing _PSC.
>
> Blaming kernel changes for platform firmware defects is not really productive.
Right, I'll reword the message and make it clear that it's firmware's issue.
>
> So this really is a workaround for defective platform firmware on the
> affected systems and it should be documented as such.
Sure.
>
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217683
> > Signed-off-by: Kai-Heng Feng <[email protected]>
> > ---
> > v2:
> > - Wording
> > - Bugzilla
> > - Add comment
> >
> > drivers/acpi/acpi_video.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> > index 62f4364e4460..bac614e9fe56 100644
> > --- a/drivers/acpi/acpi_video.c
> > +++ b/drivers/acpi/acpi_video.c
> > @@ -2027,6 +2027,13 @@ static int acpi_video_bus_add(struct acpi_device *device)
> > if (error)
> > goto err_put_video;
> >
> > +
> > + /*
> > + * Some HP laptops require ACPI video's child devices have _PS0
> > + * evaluated to have functional panel brightness control.
>
> So the comment should mention the platform firmware defect and it
> shouldn't say "some" but explicitly identify the defective platforms.
OK.
>
> > + */
> > + acpi_device_fix_up_power_extended(device);
> > +
>
> And the code change itself is simple enough, so it can be made as long
> as it is fine with Hans.
OK.
Kai-Heng
>
> > 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",
> > --