Am Samstag, dem 18.07.2026 um 11:21 +0200 schrieb Bert Karwatzki:
> Am Freitag, dem 17.07.2026 um 19:54 -0300 schrieb Leandro Ribeiro:
> >
> > On 7/17/26 11:55 AM, Alex Deucher wrote:
> > > + Some display folks
> > >
> > > On Fri, Jul 17, 2026 at 9:04 AM Bert Karwatzki <[email protected]> wrote:
> > > >
> > > > commit 860e748bddcc ("drm: ensure blend mode supported if pixel format
> > > > with alpha exposed")
> > > > introduces validate_blend_mode_for_alpha_formats() which prints
> > > > warnings for amdpgu as
> > > > amdgpu only set blend_mode_property for planes of type
> > > > DRM_PLANE_TYPE_OVERLAY. I tried to fix
> > > > this by removing he (plane->type == DRM_PLANE_TYPE_OVERLAY) check in
> > > > amdgpu_dm_plane_init():
> > > >
> > > > printk(KERN_INFO "%s: plane=%px plane->type=0x%x
> > > > plane_cap=%px\n", __func__, plane, plane->type, plane_cap);
> > > > if (plane_cap)
> > > > printk(KERN_INFO "%s: per_pixel_alpha =%u\n", __func__,
> > > > plane_cap->per_pixel_alpha);
> > > > if (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);
> > > >
> > > > printk(KERN_INFO "%s: creating alpha and blend mode
> > > > properties for plane %px\n", __func__, plane);
> > > > drm_plane_create_alpha_property(plane);
> > > > drm_plane_create_blend_mode_property(plane, blend_caps);
> > > > }
> > > >
> > > > But this does not completely silence the warnings becuase for planes of
> > > > type DRM_PLANE_TYPE_CURSOR plane_cap is NULL.
> > > > Is this a problem that should be fixed in amdgpu or is should
> > > > validate_blend_mode_for_alpha_formats() only be called
> > > > for planes of certain types?
> >
> > IMO validate_blend_mode_for_alpha_formats() should be called for all
> > types of planes. I can't think of anything special about a cursor plane
> > that would justify it being allowed to expose formats with alpha but not
> > the blend mode property.
> >
> > I'm not familiar with the AMD codebase to suggest the best fix, but the
> > driver would need some way to know whether cursor planes are exposing
> > formats with alpha.
> >
> > > >
> > > > Bert Karwatzki
> > > >
>
> So I looked through the code and found that the cursor planes are
> initiallized by
> amdgpu_dm_crtc_init() which calls amdgpu_dm_plane_init() with plane_cap =
> NULL.
> So I was able to silence the warning by introducing a dummy_plane_cap in
> amdgpu_dm_crtc_init()
> and dropping the plane->type check in amdgpu_dm_plane_init().
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> index d63688b9d93d..7fb118444d14 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> @@ -731,13 +731,17 @@ int amdgpu_dm_crtc_init(struct amdgpu_display_manager
> *dm,
> struct drm_plane *cursor_plane;
> bool has_degamma;
> int res = -ENOMEM;
> + struct dc_plane_cap dummy_cap = {
> + .type = DC_PLANE_TYPE_DCE_RGB,
> + .per_pixel_alpha = 1,
> + };
>
> cursor_plane = kzalloc_obj(*cursor_plane);
> if (!cursor_plane)
> goto fail;
>
> cursor_plane->type = DRM_PLANE_TYPE_CURSOR;
> - res = amdgpu_dm_plane_init(dm, cursor_plane, 0, NULL);
> + res = amdgpu_dm_plane_init(dm, cursor_plane, 0, &dummy_cap);
>
> acrtc = kzalloc_obj(struct amdgpu_crtc);
> if (!acrtc)
> 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 26f35434a92f..20785fb451dd 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
> @@ -1932,8 +1932,7 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager
> *dm,
> if (res)
> return res;
>
> - if (plane->type == DRM_PLANE_TYPE_OVERLAY &&
> - plane_cap && plane_cap->per_pixel_alpha) {
> + if (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);
>
> One can probably also omit the .type field in the dummy_cap struct and
> also does not have to check if plance_cap is NULL anymore.
>
> Bert Karwatzki
This might seem problematic as this unconditionally sets per_pixel_alpha = true
for cursor planes,
but currently the only pixel format used for cursor planes in amdgpu is
DRM_FORMAT_ARGB8888:
$ grep -B 1 -A 3 'cursor_formats\[\]'
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
static const u32 cursor_formats[] = {
DRM_FORMAT_ARGB8888
};
Bert Karwatzki
