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drm/amd/display: Fix backlight max_brightness to match exported range

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[Why]
FWTS autobrightness fails on eDP panels because actual_brightness can
read higher than the advertised max_brightness (e.g. 63576 vs 62451).

The conversion helpers expose the firmware PWM range to userspace as
[0..max].  But max_brightness is advertised as (max - min), which is
smaller.  So reading the level can return a value above max_brightness.

This regressed in commit 4b61b8a390 ("drm/amd/display: Add debugging
message for brightness caps"), which changed max_brightness to
(max - min) and undid commit 8dbd72cb79 ("drm/amd/display: Export full
brightness range to userspace").

[How]
Advertise max_brightness as max, and scale the initial AC/DC brightness
against max too.  Update the KUnit expectations to match.

Fixes: 4b61b8a390 ("drm/amd/display: Add debugging message for brightness caps")
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit bd9e2b5b0473c75abc0f4134dfe79ecbfb16610d)
Cc: stable@vger.kernel.org
This commit is contained in:
Mario Limonciello 2026-06-29 15:27:00 -05:00 committed by Alex Deucher
parent 9b3aa1dec7
commit f1b5d8f9cc
1 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
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@ -5563,11 +5563,11 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
caps = &dm->backlight_caps[aconnector->bl_idx];
if (get_brightness_range(caps, &min, &max)) {
if (power_supply_is_system_supplied() > 0)
props.brightness = DIV_ROUND_CLOSEST((max - min) * caps->ac_level, 100);
props.brightness = DIV_ROUND_CLOSEST(max * caps->ac_level, 100);
else
props.brightness = DIV_ROUND_CLOSEST((max - min) * caps->dc_level, 100);
props.brightness = DIV_ROUND_CLOSEST(max * caps->dc_level, 100);
/* min is zero, so max needs to be adjusted */
props.max_brightness = max - min;
props.max_brightness = max;
drm_dbg(drm, "Backlight caps: min: %d, max: %d, ac %d, dc %d\n", min, max,
caps->ac_level, caps->dc_level);
} else