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>

2 files changed, 7 insertions, 7 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c
index 11d54897a894..ca60c72855fd 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c
@@ -407,12 +407,12 @@ void amdgpu_dm_backlight_fill_props(const struct amdgpu_dm_backlight_caps *caps,
 
 	if (get_brightness_range(caps, &min, &max)) {
 		if (is_system_supplied)
-			props->brightness = DIV_ROUND_CLOSEST((max - min) * caps->ac_level,
+			props->brightness = DIV_ROUND_CLOSEST(max * caps->ac_level,
 							       100);
 		else
-			props->brightness = DIV_ROUND_CLOSEST((max - min) * caps->dc_level,
+			props->brightness = DIV_ROUND_CLOSEST(max * caps->dc_level,
 							       100);
-		props->max_brightness = max - min;
+		props->max_brightness = max;
 	} else {
 		props->brightness = MAX_BACKLIGHT_LEVEL;
 		props->max_brightness = MAX_BACKLIGHT_LEVEL;
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c
index adb896022a27..8ebc0f263e3e 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c
@@ -799,8 +799,8 @@ static void dm_test_backlight_fill_props_ac_linear(struct kunit *test)
 	amdgpu_dm_backlight_fill_props(&caps, true, false, &props);
 
 	KUNIT_EXPECT_EQ(test, props.brightness,
-			 DIV_ROUND_CLOSEST((max - min) * caps.ac_level, 100));
-	KUNIT_EXPECT_EQ(test, props.max_brightness, max - min);
+			 DIV_ROUND_CLOSEST(max * caps.ac_level, 100));
+	KUNIT_EXPECT_EQ(test, props.max_brightness, max);
 	KUNIT_EXPECT_EQ(test, props.scale, BACKLIGHT_SCALE_LINEAR);
 	KUNIT_EXPECT_EQ(test, props.type, BACKLIGHT_RAW);
 }
@@ -825,8 +825,8 @@ static void dm_test_backlight_fill_props_dc_nonlinear(struct kunit *test)
 	amdgpu_dm_backlight_fill_props(&caps, false, true, &props);
 
 	KUNIT_EXPECT_EQ(test, props.brightness,
-			 DIV_ROUND_CLOSEST((max - min) * caps.dc_level, 100));
-	KUNIT_EXPECT_EQ(test, props.max_brightness, max - min);
+			 DIV_ROUND_CLOSEST(max * caps.dc_level, 100));
+	KUNIT_EXPECT_EQ(test, props.max_brightness, max);
 	KUNIT_EXPECT_EQ(test, props.scale, BACKLIGHT_SCALE_NON_LINEAR);
 	KUNIT_EXPECT_EQ(test, props.type, BACKLIGHT_RAW);
 }