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

[Thorsten Leemhuis]

On 5/15/26 13:47, Stefan Seyfried wrote:
> 
> 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

FWIW: Here are two bug reports that contain proposed fixes for what
might or might not be the issue your face:

https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16043
https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16015

Ciao,  Thorsten

>>         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,