Re: [PATCH RESEND 1/2] drm/amd/display: Use linear backlight curve in power module

[Ray Wu <ray.wu@amd.com>]

Hi Mathew,

We have a similar change has already been merged into asdn DC 3.2.400 
release.
     commit: drm/amd/display: map PWM brightness through custom 
backlight curve

Could you give it a try? If you still see any other issues, please feel 
free to send an updated patch.
Thanks!

On 9/17/2026 3:11 AM, Matthew Schwartz wrote:
> 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;
>   		/*