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 <kai.heng.feng@xxxxxxxxxxxxx>
---
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
