[PATCH 0/2] Avoid creating acpi_video0 on desktop APUs

[Mario Limonciello]

In kernel 6.1 the backlight registration code was overhauled so that
at most one backlight device got registered. As part of this change
there was code added to cover the "nomodeset" case to still allow
making an acpi_video0 device if the BIOS contained backlight control
methods.

This fallback logic however is failing on the BIOS from a number of
motherboard manufacturers supporting Ryzen APUs.  What happens is
the amdgpu driver finishes registration and as expected doesn't
create a backlight control device since no eDP panels are connected
to a desktop.

Then 8 seconds later the ACPI video detection code creates an
acpi_video0 device that is non-operational. GNOME then creates a
backlight slider.

To avoid this situation from happening add support for video drivers
to notify the ACPI video detection code that no panel was detected.

To reduce the risk of regressions on multi-GPU systems:
* only use this logic when the system is reported as a desktop enclosure.
* in the amdgpu code only report into this for APUs.

Mario Limonciello (2):
  ACPI: video: Allow GPU drivers to report no panels
  drm/amd/display: Report to ACPI video if no panels were found

 drivers/acpi/acpi_video.c                         | 12 ++++++++++++
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  4 ++++
 include/acpi/video.h                              |  1 +
 3 files changed, 17 insertions(+)

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2.34.1