[PATCH RFT 0/3] drm/amd/display: Fix the doubled AUX backlight minimum on the custom curve

[Hugo Sales]

With an ATIF custom brightness curve, convert_brightness_from_user()
adds the minimum brightness of an AUX backlight panel twice, so a
request for 0 lands well above the minimum. Patch 1 fixes that, patch 2
drops the argument the fix leaves unused, and patch 3 adds a KUnit test

I'm preparing a separate series that stops rounding the backlight level
to 8 bits and the luminance to a whole percent, and removes
convert_custom_brightness() along the way. This series stays minimal so
it can go in on its own first. If you'd rather take it all at once, I
can fold this fix into that series instead

PWM went through the same code until commit d422a66847a9
("drm/amd/display: map PWM brightness through custom backlight curve"),
which is how I found it. My laptop drives its panel over PWM, so I
tested this with KUnit and with the amdgpu_dm_brightness trace on 7.2.9,
before that commit. A Tested-by from someone with an AUX backlight panel
and an ATIF curve would help: brightness 0 should give the panel's
minimum

I also wonder whether the ATIF curve is meant for AUX at all. My
understanding is that on PWM the curve is meant to linearize the panel's
response to the PWM signal, and that an AUX panel gets a target in nits
and drives its own backlight to reach it. So it seems odd to me that AUX
gets the curve too. Is it meant for AUX, or is there a different curve
for AUX panels? This series keeps applying it on AUX, as the code does
today

Signed-off-by: Hugo Sales <hugo@xxxxxxx>
---
Hugo Sales (3):
      drm/amd/display: Add the AUX backlight minimum once on the custom curve
      drm/amd/display: Drop the unused min argument of convert_custom_brightness()
      drm/amd/display: Add a KUnit test for the custom curve minimum

 .../amd/display/amdgpu_dm/amdgpu_dm_backlight.c    | 14 ++---
 .../amd/display/amdgpu_dm/amdgpu_dm_backlight.h    |  3 +-
 .../amdgpu_dm/tests/amdgpu_dm_backlight_test.c     | 70 +++++++++++++++++-----
 3 files changed, 62 insertions(+), 25 deletions(-)
---
base-commit: ba496bb837882eb1af58f41572fc289e46c77b8c
change-id: 20261102-amdgpu-aux-curve-min-3f6b2a1c9d4e

Best regards,
--  
Hugo Sales <hugo@xxxxxxx>