Re: [PATCH v3 3/3] drm/amd/display: advertise PIXEL_NONE as blend mode for DCE generations

On 13/08/2026 16:44, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Calling drm_plane_create_blend_mode_property() without PREMULTI support triggers a kernel warning (WARN_ON) and fails to create the property.
> --
>
> --- Patch [3]: [PATCH v3 3/3] drm/amd/display: advertise PIXEL_NONE as blend mode for DCE generations ---
> commit 44681caffc8bcfc7085bcfe1ec288a0eafc8c992
> Author: Melissa Wen <[email protected]>
>
> drm/amd/display: advertise PIXEL_NONE as blend mode for DCE generations
>
> This commit changes the blend mode property creation for primary planes on
> DCE generations. It modifies the driver to create the blend mode property
> with PIXEL_NONE only, instead of the DRM default PREMULTI mode.
>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
>> index 423e3cd7b9c98..e02cbafc8c5d0 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> [ ... ]
>> @@ -2208,14 +2208,18 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
> [ ... ]
>> -	if ((plane->type == DRM_PLANE_TYPE_OVERLAY ||
>> -	     plane->type == DRM_PLANE_TYPE_PRIMARY) &&
>> -	    plane_cap && plane_cap->per_pixel_alpha &&
>> -	    plane_cap->type == DC_PLANE_TYPE_DCN_UNIVERSAL) {
>> +	if (plane_cap && plane_cap->type != DC_PLANE_TYPE_DCN_UNIVERSAL) {
>> +		drm_plane_create_blend_mode_property(plane, BIT(DRM_MODE_BLEND_PIXEL_NONE));
> [Severity: High]
> Does this trigger a kernel warning and fail to create the property?
>
> Looking at drm_plane_create_blend_mode_property() in drm_blend.c, the DRM
> core explicitly enforces that DRM_MODE_BLEND_PREMULTI must be supported:
>
> int drm_plane_create_blend_mode_property(struct drm_plane *plane,
> 					 unsigned int supported_modes)
> {
> 	...
> 	if (WARN_ON((supported_modes & ~valid_mode_mask) ||
> 		    ((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0)))
> 		return -EINVAL;
> 	...
> }
>
> Since amdgpu_dm_plane_init() now passes only BIT(DRM_MODE_BLEND_PIXEL_NONE),
> this will trigger the WARN_ON and return -EINVAL during device probe,
> meaning the property is not created at all.

No, you are probably looking at an outdated codebase.

Other blend modes are supported since:

9813e158d13d5 ("drm/drm_blend: allow blend mode property without 
PREMULTI") in drm-misc-next.

Melissa

>
>> +	} else if ((plane->type == DRM_PLANE_TYPE_OVERLAY ||
>> +		    plane->type == DRM_PLANE_TYPE_PRIMARY) &&
>> +		   plane_cap && plane_cap->per_pixel_alpha) {
>>   		unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
>>   					  BIT(DRM_MODE_BLEND_PREMULTI) |
>>   					  BIT(DRM_MODE_BLEND_COVERAGE);