[REGRESSION] bisected: 7.1rc1 breaks backlight control on Thinkpad T480

[Stefan Seyfried]

Hi all,

I found that 7.1rc1 broke the backlight control on my Thinkpad T480.
Bisected it to

> 40d2f5820951dee818d05c14677277048bd85f9f is the first bad commit
> commit 40d2f5820951dee818d05c14677277048bd85f9f
> Author: Suraj Kandpal <suraj.kandpal@xxxxxxxxx>
> Date:   Tue Feb 24 08:43:22 2026 +0530
>
>     drm/i915/backlight: Remove try_vesa_interface
>     
>     Some panels need VESA DPCD AUX backlight but VBT says otherwise.
>     This is why we try with Intel backlight interface over VESA backlight
>     interface. This causes a blankout on such panels without any fallback
>     mechanism.
>     Remove try_vesa_interface and use VESA AUX backlight interface as a
>     fallback mechanism.
>     While at in sneak in a small comment cleanup too.
>     
>     Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/15679
>     Signed-off-by: Suraj Kandpal <suraj.kandpal@xxxxxxxxx>
>     Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
>     Link: https://patch.msgid.link/20260224031322.2568874-1-suraj.kandpal@xxxxxxxxx
>
>  drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 19 +++++++------------
>  1 file changed, 7 insertions(+), 12 deletions(-)

Please revert :-)

Best regards,
--
Stefan Seyfried

"For a successful technology, reality must take precedence over
 public relations, for nature cannot be fooled." -- Richard Feynman