[PATCH] Revert "drm/amd/display: Fix backlight max_brightness to match exported range"

This reverts commit 1191285ecb4233e5bf907da7e9394d7999055566.

This patch is apparently missing a dependency from 7.2 as users have not
reported any regressions with 7.2-rc, but there are regressions on 7.1.

The regression manifests as inconsistent lower brightness at the top end
(e.g., around 98%).

Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5562
Signed-off-by: Alex Deucher <[email protected]>
Cc: Thorsten Leemhuis <[email protected]>
Cc: Sergio Callegari <[email protected]>
Cc: Mario Limonciello <[email protected]>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

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 40d82a3eeec0..6f9d4bea3379 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -5401,11 +5401,11 @@ 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 * caps->ac_level, 100);
+			props.brightness = DIV_ROUND_CLOSEST((max - min) * caps->ac_level, 100);
 		else
-			props.brightness = DIV_ROUND_CLOSEST(max * caps->dc_level, 100);
+			props.brightness = DIV_ROUND_CLOSEST((max - min) * caps->dc_level, 100);
 		/* min is zero, so max needs to be adjusted */
-		props.max_brightness = max;
+		props.max_brightness = max - min;
 		drm_dbg(drm, "Backlight caps: min: %d, max: %d, ac %d, dc %d\n", min, max,
 			caps->ac_level, caps->dc_level);
 	} else
-- 
2.55.0