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

Klymenko, Anatoliy
2025-11-13T23:03:56Z

[AMD Official Use Only - AMD Internal Distribution Only]

Hi Sean,

Thank you for the patch.

> -----Original Message-----
> From: Sean Anderson <sean.anderson@linux.dev>
> Sent: Thursday, November 13, 2025 12:37 PM
> To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>; Tomi Valkeinen
> <tomi.valkeinen@ideasonboard.com>; dri-devel@lists.freedesktop.org
> Cc: linux-kernel@vger.kernel.org; Mike Looijmans <mike.looijmans@topic.nl>;
> David Airlie <airlied@gmail.com>; Thomas Zimmermann
> <tzimmermann@suse.de>; Maarten Lankhorst
> <maarten.lankhorst@linux.intel.com>; Klymenko, Anatoliy
> <Anatoliy.Klymenko@amd.com>; Maxime Ripard <mripard@kernel.org>; linux-
> arm-kernel@lists.infradead.org; Simona Vetter <simona@ffwll.ch>; Simek,
> Michal <michal.simek@amd.com>; Sean Anderson
> <sean.anderson@linux.dev>
> Subject: [PATCH 3/3] drm: zynqmp: Add blend mode property to graphics plane
>
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
>
>
> 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@linux.dev>
> ---
>
> 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