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

[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 4b61b8a39051 ("drm/amd/display: Add debugging
message for brightness caps"), which changed max_brightness to
(max - min) and undid commit 8dbd72cb7900 ("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: 4b61b8a39051 ("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

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 18145d78334fdae198530ae0ef1f7bf913b4ee0f..ff337de44f7ad1203d50d952234015093680f193 100644 (file)
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -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