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

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Message-Id: <20230719023223.2971481-1-kai.heng.feng@canonical.com>
Date:   Wed, 19 Jul 2023 10:32:23 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     rafael@...nel.org, lenb@...nel.org, hdegoede@...hat.com
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] ACPI: video: Put ACPI video and its child devices to D0 at boot

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@...onical.com>
---
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