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

On 8/25/26 10:06, Melissa Wen wrote:
> 
> 
> On 24/08/2026 23:02, Viktor Jägersküpper wrote:
>> On 8/24/26 22:38, Viktor Jägersküpper wrote:
>>> [ Adding Timur ]
>>>
>>> On 8/13/26 16:30, Melissa Wen wrote:
>>>> DCE can support PREMULTI and COVERAGE blend mode depending on its
>>>> generation, however current driver implementation either doesn't expose
>>>> more than primary and cursor plane, or doesn't program registers for
>>>> any
>>>> blend mode other than PIXEL_NONE. To fix the missing-blend-mode-prop
>>>> warning according to current DCE plane caps, create blend mode property
>>>> with PIXEL_NONE only for primary planes, instead of the DRM default
>>>> PREMULTI.
>>>>
>>>> Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel
>>>> format with alpha exposed")
>>>> Reviewed-by: Leandro Ribeiro <[email protected]>
>>>> Signed-off-by: Melissa Wen <[email protected]>
>>>>
>>>> ---
>>>> v3:
>>>> - fix indentation (Alex H)
>>>> ---
>>>>   .../amd/display/amdgpu_dm/amdgpu_dm_plane.c    | 18 ++++++++++
>>>> +-------
>>>>   1 file changed, 11 insertions(+), 7 deletions(-)
>>>>
>>>> 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 ab9bbe8ca333..3b5b6943b67d 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
>>>> @@ -1923,14 +1923,18 @@ int amdgpu_dm_plane_init(struct
>>>> amdgpu_display_manager *dm,
>>>>       if (res)
>>>>           return res;
>>>>   -    /* TODO: Check which blend modes are supported in DCE-generation
>>>> -     * planes, i.e. DC_PLANE_TYPE_DCE_RGB/UNDERLAY and expose blend
>>>> mode
>>>> -     * property accordingly.
>>>> +    /* Blend mode support varies on DCE generations according to HW
>>>> caps
>>>> +     * and number of planes per CRTC. However, as current driver
>>>> +     * implementation only creates one primary and one cursor plane
>>>> per
>>>> +     * CRTC for DCE (overlay is only created if
>>>> +     * DC_PLANE_TYPE_DCN_UNIVERSAL), the primary plane blend mode
>>>> ends up
>>>> +     * being always PIXEL_NONE across DCE versions.
>>>>        */
>>>> -    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));
>>>> +    } 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);
>>> With this patch applied to the mainline kernel, my display freezes when
>>> Kwin is started (either by SDDM or by launching a KDE Plasma session).
>>> GDM and Gnome work fine. The journal doesn't have much information, it's
>>> mainly this:
> 
> I suspect KDE is not interpreting correctly the blend mode, but I think
> we can
> keep it working as before by adding PREMULTI. In the end there is no
> overlay
> plane for DCE, and PIXEL_NONE and PREMULTI are equivalent when one
> primary is composed on top of a black background.
> 
> Can you replace this commit by the patch attached?
> It might solve the issue as long as background continues being black.
> I didn't apply it to drm-misc, so let me know how does this new patch works
> on your side.
The attached patch solves the issue, I tested both KDE/SDDM and
Gnome/GDM, the warnings are gone as expected. You can add:

Tested-by: Viktor Jägersküpper <[email protected]>

Thanks,
Viktor