RE: [PATCH 3/3] drm: zynqmp: Add blend mode property to graphics plane

[Klymenko, Anatoliy]

[AMD Official Use Only - AMD Internal Distribution Only]

Hi Sean,

Thank you for the patch.

> -----Original Message-----
> From: Sean Anderson <sean.anderson@xxxxxxxxx>
> Sent: Thursday, November 13, 2025 12:37 PM
> To: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>; Tomi Valkeinen
> <tomi.valkeinen@xxxxxxxxxxxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; Mike Looijmans <mike.looijmans@xxxxxxxx>;
> David Airlie <airlied@xxxxxxxxx>; Thomas Zimmermann
> <tzimmermann@xxxxxxx>; Maarten Lankhorst
> <maarten.lankhorst@xxxxxxxxxxxxxxx>; Klymenko, Anatoliy
> <Anatoliy.Klymenko@xxxxxxx>; Maxime Ripard <mripard@xxxxxxxxxx>; linux-
> arm-kernel@xxxxxxxxxxxxxxxxxxx; Simona Vetter <simona@xxxxxxxx>; Simek,
> Michal <michal.simek@xxxxxxx>; Sean Anderson
> <sean.anderson@xxxxxxxxx>
> Subject: [PATCH 3/3] drm: zynqmp: Add blend mode property to graphics plane
>
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>
>
> When global alpha is enabled, per-pixel alpha is ignored. Allow
> userspace to explicitly specify whether to use per-pixel alpha by
> exposing it through the blend mode property. I'm not sure whether the
> per-pixel alpha is pre-multiplied or not [1], but apparently it *must* be
> pre-multiplied so I guess we have to advertise it.
>
> [1] All we get is "The alpha value available with the graphics stream
>     will define the transparency of the graphics."
>
> Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>
> ---
>
>  drivers/gpu/drm/xlnx/zynqmp_kms.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_kms.c
> b/drivers/gpu/drm/xlnx/zynqmp_kms.c
> index 456ada9ac003..fa1cfc16db36 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_kms.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_kms.c
> @@ -61,6 +61,13 @@ static int zynqmp_dpsub_plane_atomic_check(struct
> drm_plane *plane,
>         if (!new_plane_state->crtc)
>                 return 0;
>
> +       if (new_plane_state->pixel_blend_mode !=
> DRM_MODE_BLEND_PIXEL_NONE &&
> +           new_plane_state->alpha >> 8 != 0xff) {
> +               drm_dbg_kms(plane->dev,
> +                           "Plane alpha must be 1.0 when using pixel alpha\n");
> +               return -EINVAL;
> +       }
> +
>         crtc_state = drm_atomic_get_crtc_state(state, new_plane_state->crtc);
>         if (IS_ERR(crtc_state))
>                 return PTR_ERR(crtc_state);
> @@ -117,9 +124,13 @@ static void
> zynqmp_dpsub_plane_atomic_update(struct drm_plane *plane,
>
>         zynqmp_disp_layer_update(layer, new_state);
>
> -       if (plane->index == ZYNQMP_DPSUB_LAYER_GFX)
> -               zynqmp_disp_blend_set_global_alpha(dpsub->disp, true,
> +       if (plane->index == ZYNQMP_DPSUB_LAYER_GFX) {
> +               bool blend = plane->state->pixel_blend_mode ==
> +                            DRM_MODE_BLEND_PIXEL_NONE;
> +
> +               zynqmp_disp_blend_set_global_alpha(dpsub->disp, blend,
>                                                    plane->state->alpha >> 8);
> +       }
>
>         /*
>          * Unconditionally enable the layer, as it may have been disabled
> @@ -179,9 +190,18 @@ static int zynqmp_dpsub_create_planes(struct
> zynqmp_dpsub *dpsub)
>                         return ret;
>
>                 if (i == ZYNQMP_DPSUB_LAYER_GFX) {
> +                       unsigned int blend_modes =
> +                               BIT(DRM_MODE_BLEND_PIXEL_NONE) |
> +                               BIT(DRM_MODE_BLEND_PREMULTI);

| BIT(DRM_MODE_BLEND_COVERAGE) - this is what implemented in the hardware.

> +
>                         ret = drm_plane_create_alpha_property(plane);
>                         if (ret)
>                                 return ret;
> +
> +                       ret = drm_plane_create_blend_mode_property(plane,
> +                                                                  blend_modes);
> +                       if (ret)
> +                               return ret;
>                 }
>         }
>
> --
> 2.35.1.1320.gc452695387.dirty

Thank you,
Anatoliy