[SRU][R][PATCH 0/1] drm/i915: Restore VESA backlight interface

[Krystian Kaniewski]

BugLink: https://bugs.launchpad.net/bugs/2161309

SRU Justification:

[Impact]

Ubuntu kernel 7.0.0-28.28 includes commit 40d2f5820951
("drm/i915/backlight: Remove try_vesa_interface").

That change causes an internal display backlight regression on systems
whose panel advertises VESA AUX backlight support but actually requires
the Intel/PWM backlight path. Brightness writes complete and the value
under /sys/class/backlight/intel_backlight changes, but the physical
screen brightness does not change.

[Fix]

Cherry-pick upstream commit:

f30fddb44023 ("Revert \"drm/i915/backlight: Remove try_vesa_interface\"")

This reverts commit:

40d2f5820951 ("drm/i915/backlight: Remove try_vesa_interface")

The revert restores the try_vesa_interface gate. This prevents i915
from selecting the VESA AUX backlight path as an unconditional fallback
on panels whose VBT indicates that the Intel backlight interface should
be used.

[Test Case]

Build tested

[Where problems could occur]

The change affects the i915 backlight interface-selection logic for
internal eDP displays.

A regression could cause brightness control to stop working, select an
incorrect backlight interface, or restore the wrong brightness level
after suspend and resume.

The regression potential is considered limited because an equivalent
change has already been merged and reviewed upstream.

[Other Info]

The upstream revert is present as f30fddb44023. An equivalent
cherry-pick, 2914709c9141, was included before Linux 7.1-rc7.

Suraj Kandpal (1):
  Revert "drm/i915/backlight: Remove try_vesa_interface"

 .../drm/i915/display/intel_dp_aux_backlight.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

-- 
2.53.0