linux-kernel - [PATCH v3] ACPI: video: Put ACPI video and its child devices to D0 at boot

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Message-Id: <20230721152143.3108017-1-kai.heng.feng@canonical.com>
Date:   Fri, 21 Jul 2023 23:21:43 +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 v3] ACPI: video: Put ACPI video and its child devices to D0 at boot

Screen brightness can only be changed once on HP ZBook Fury 16 G10.

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 this device because _PSC is missing,
which violates ACPI spec 6.3, section 7.3.6. Commit 7cd8407d53ef
("ACPI / PM: Do not execute _PS0 for devices without _PSC during
initialization") tried to workaround missing _PSC on defective
firmwares, but got reverted because of regression.

So the safest approach is to 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>
---
v3:
 - Wording change to make it clear it's a firmware issue.
 - Specify the device name in comment.

v2:
 - Wording
 - Bugzilla
 - Add comment

 drivers/acpi/acpi_video.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 62f4364e4460..1732780a672b 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -2027,6 +2027,12 @@ static int acpi_video_bus_add(struct acpi_device *device)
 	if (error)
 		goto err_put_video;
 
+	/*
+	 * HP ZBook Fury 16 G10 requires 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