[PATCH v2] ACPI: video: Put ACPI video and its child devices to D0 at boot

[Kai-Heng Feng]

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