[PATCH RFC 0/3] drm/amd/display: Check the ATIF backlight curve

[Hugo Sales]

The ATIF custom brightness curve comes from firmware, and amdgpu uses it
without checking that its points rise. Patch 1 checks the curve once at
probe. It drops a curve whose signals fall, caps a luminance over 100%
at 100%, and raises a luminance that falls. When it changes the curve,
it warns about a firmware bug. Patch 2 adds KUnit tests. Patch 3
turns the debug message for an invalid signal range into a warning
too, so users have something to report

I haven't seen a curve this would change. My laptop's curve passes, and
so do 240 static curves I found in public ACPI dumps of 15 laptop
models. On many Ryzen laptops the firmware builds the curve at boot,
though, and a scan of the tables can't see those. The bug reports I
found of an ASUS curve over 100% turned out to be a different overflow
bug. Sashiko flagged a luminance over 100% while reviewing [1], and I
extended the check to falling points. So this is hardening. If you'd
rather not carry the check, I'm fine with dropping it

It applies on top of "drm/amd/display: Stop rounding backlight levels
to whole percents" [1]. Patch 2's brightness checks use the curve
mapping from that series

[1] https://lore.kernel.org/lkml/20261103-backlight-curve-rfc-v1-0-6e4813a8f2eb@xxxxxxx/

Signed-off-by: Hugo Sales <hugo@xxxxxxx>
---
Hugo Sales (3):
      drm/amd/display: Repair or drop a bad ATIF backlight curve
      drm/amd/display: Add KUnit tests for the ATIF backlight curve check
      drm/amd/display: Warn about an invalid ATIF backlight signal range

 .../amd/display/amdgpu_dm/amdgpu_dm_backlight.c    |  50 +++++-
 .../amdgpu_dm/tests/amdgpu_dm_backlight_test.c     | 184 +++++++++++++++++++++
 2 files changed, 232 insertions(+), 2 deletions(-)
---
base-commit: ba496bb837882eb1af58f41572fc289e46c77b8c
change-id: 20261103-backlight-curve-validate-243c4ce9692c
prerequisite-message-id: <20261103-amdgpu-aux-curve-min-v1-0-62119efdcc6d@xxxxxxx>
prerequisite-patch-id: 0eefd25bf4ad8f6d779c7a0b0a63f84969b67fca
prerequisite-patch-id: 016515673f79f623de1e50dd513e5440587329b6
prerequisite-patch-id: ba453baf376b5410d66feacb1956eea933042ae8
prerequisite-message-id: <20261103-backlight-curve-rfc-v1-0-6e4813a8f2eb@xxxxxxx>
prerequisite-patch-id: ab08642e6487dac872fecb986cee493826c90ca9
prerequisite-patch-id: 615ae71fc87a132500083a791977cedffb5c5535
prerequisite-patch-id: d5f11b9531761fbfd4103cebc6f0e9403cd53772
prerequisite-patch-id: 95660ed7df12918c00809bf09d9d979c597bcbb6
prerequisite-patch-id: 4bf24c99ce3da811000e96e67ca6b93df79eb964
prerequisite-patch-id: 33257e757b334f4a8cb44b4efc24a3f3cd000307
prerequisite-patch-id: dec6b61e59750a963d14cb6905cb76a4cb76f77c
prerequisite-patch-id: f1fe27995f1a36d9382674eb9951ea5fe5f18a91

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