linux-kernel - [REGRESSION] Missing nouveau backlight control on 6.2.x kernel

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Date:   Fri, 17 Mar 2023 11:04:12 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     linux-kernel@...r.kernel.org, regressions@...ts.linux.dev,
        dri-devel@...ts.freedesktop.org
Subject: [REGRESSION] Missing nouveau backlight control on 6.2.x kernel

Hi,

we've received a regression report on openSUSE Bugzilla about the
missing backlight control of nouveau device:
  https://bugzilla.opensuse.org/show_bug.cgi?id=1209296

On 6.1, with acpi_video=native option, the system provided
/sys/class/backlight/nv_backlight entry.

On 6.2, with acpi_video=native option, there is no entry in
/sys/class/backlight.  And without acpi_video option, it falls back to
/sys/class/backlight/acpi_video0, which doesn't work as expected.

Hans, could you check whether the recent change in video_detect.c (or
anything else) may influence on this?  My gut feeling is that the
culprit could be rather some change in nouveau (so dri-devel is
Cc'ed), but I'm not entirely sure...

Thanks!

Takashi