[PATCH 1/2] [FOR-UPSTREAM] drm/amd/display: Use linear backlight curve in power module

[PATCH 1/2] [FOR-UPSTREAM] drm/amd/display: Use linear backlight curve in power module

[Matthew Schwartz]

amdgpu_dm already applies the ATIF custom brightness curve in
convert_custom_brightness() before handing the level to the power
module. The power module then builds its own percent to PWM LUT from
the same ATIF data in initialize_backlight_caps() and applies the curve
a second time. On the Lenovo Legion Go S this maps the bottom 40% of the
brightness range to under 12% PWM, where the panel no longer visibly
changes.

Tell the power module to use its linear curve so the PWM is a straight
rescale of the level DM computed, matching the behavior before the power
module took over backlight programming.

Fixes: 3c108046e1d6 ("drm/amd/display: Add power module on Linux")
Signed-off-by: Matthew Schwartz <matthew.schwartz@linux.dev>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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 ca795cda8084..63acefc0acfb 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -455,7 +455,7 @@ STATIC_IFN_KUNIT int amdgpu_dm_init_power_module(struct amdgpu_display_manager *
 			!(amdgpu_dc_feature_mask & DC_DISABLE_FRACTIONAL_PWM_MASK);
 		init_data[i].use_custom_backlight_caps = false;
 		init_data[i].custom_backlight_caps_config_no = 0;
-		init_data[i].use_linear_backlight_curve = false;
+		init_data[i].use_linear_backlight_curve = true;
 		init_data[i].def_varibright_enable = 0;
 		init_data[i].varibright_level = 0;
 		/*
-- 
2.55.0