Re: [PATCH v2 0/3] drm/atomic-state-helper: fixes for blend-mode-prop warning

On 04/08/2026 16:00, Melissa Wen wrote:
> PREMULTI was the default DRM blend mode until 9813e158d13d
> ("drm/drm_blend: allow blend mode property without PREMULTI") introduced
> the possibility of exposing the blend mode property without PREMULTI
> being supported. However, __drm_atomic_helper_plane_state_init() still
> resets pixel_blend_mode to PREMULTI (hardcoded), ignoring the supported
> mode in this property. In the same series, 860e748bddcc ("drm: ensure
> blend mode supported if pixel format with alpha exposed") starts warning
> drivers that supports alpha formats in a given planes but doesn't
> support blend mode property, which includes AMD primary and cursor
> planes.
>
> For AMD DCN families, overlay and primary planes support the three blend
> modes, and therefore PREMULTI is still the default mode. So the warn can
> be fixed by just creating blend mode properties for primary planes too.
> PREMULTI is the default/unique mode for cursor planes in DCN and DCE
> driver. However, looks like PIXEL_NONE is the unique blend mode
> supported by DCE-generation driver. I don't have the hardware to check
> it out, but looking at the code I understand that, even if the hardware
> can do PREMULTI or COVERAGE, the way it programs registers doesn't make
> these other blend modes actually available.

Hello,

As this series mostly fixes AMD display driver, can I get an ack from 
AMD folks?

Thanks in advance,

Melissa

>
> Bearing this in mind, this series is organized as follow:
>
> - Patch 1 fixes the pixel_blend_mode reset when the blend mode property
>    is advertised without PREMULTI support. It's needed for AMD
>    DCE-generation (patch 3) and I think with this we can also remove a
>    workaround in nouveau nv50_wndw_default_state() caused by the
>    hardcoded PREMULTI default value [1].
>
> - Patch 2 fixes the missing-blend-mode-property warning for DCN primary
>    plane and for DCN+DCE cursor plane.
>
> - Patch 3 fixes the warning for DCE primary plane, but I detached this
>    solution from the previous patch because I don't have hardware to
>    validate if my assumption about PIXEL_NONE-only is correct.
>
> [1] https://lore.kernel.org/dri-devel/[email protected]/
>
> [v1]: https://lore.kernel.org/dri-devel/[email protected]/
> Changes:
> - new patch for pixel_blend_mode default value other than PREMULTI.
> - remove DCE11 which supports per_pixel_alpha but doesn't support DCN_UNIVERSAL_PLANE.
> - new patch for the primary plane blend mode on DCE-generations
>
> Best Regards,
>
> Melissa
>
> Melissa Wen (3):
>    drm/atomic-state-helper: set pixel_blend_mode to prop default on reset
>    drm/amd/display: fix missing blend-mode-prop warning for DCN
>    drm/amd/display: advertise PIXEL_NONE as blend mode for DCE
>      generations
>
>   .../amd/display/amdgpu_dm/amdgpu_dm_plane.c   | 22 +++++++++++++++++--
>   drivers/gpu/drm/drm_atomic_state_helper.c     |  7 ++++++
>   2 files changed, 27 insertions(+), 2 deletions(-)
>