linux-kernel - [REGRESSION] amdgpu: thinkpad e495 backlight brightness resets after suspend

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Message-Id: <D6HQK0PSRVBC.XEUGZC9N1O5K@svmhdvn.name>
Date: Sat, 21 Dec 2024 17:35:37 -0500
From: "Siva Mahadevan" <me@...hdvn.name>
To: <alexander.deucher@....com>
Cc: <regressions@...ts.linux.dev>, <stable@...r.kernel.org>,
 <amd-gfx@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
 <Xinhui.Pan@....com>, <christian.koenig@....com>
Subject: [REGRESSION] amdgpu: thinkpad e495 backlight brightness resets
 after suspend

#regzbot introduced: 99a02eab8

Observed behaviour:
linux-stable v6.12.5 has a regression on my thinkpad e495 where
suspend/resume of the laptop results in my backlight brightness settings
to be reset to some very high value. After resume, I'm able to increase
brightness further until max brightness, but I'm not able to decrease it
anymore.

Behaviour prior to regression:
linux-stable v6.12.4 correctly maintains the same brightness setting on
the backlight that was set prior to suspend/resume.

Notes:
I bisected this issue between v6.12.4 and v6.12.5 to commit 99a02eab8
titled "drm/amdgpu: rework resume handling for display (v2)".

Hardware:
* lenovo thinkpad e495
* AMD Ryzen 5 3500U with Radeon Vega Mobile Gfx
* VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
  Picasso/Raven 2 [Radeon Vega Series / Radeon Vega Mobile Series]
  (rev c2)