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

Klymenko, Anatoliy
2025-11-13T23:59:45Z

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Klymenko, Anatoliy
> Sent: Thursday, November 13, 2025 3:04 PM
> To: 'Sean Anderson' <sean.anderson@linux.dev>; 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>; Maxime Ripard <mripard@kernel.org>;
> linux-arm-kernel@lists.infradead.org; Simona Vetter <simona@ffwll.ch>; Simek,
> Michal <michal.simek@amd.com>
> Subject: RE: [PATCH 3/3] drm: zynqmp: Add blend mode property to graphics
> plane
>
> 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;

I would suggest adding
|| !plane->state->fb->format->has_alpha;
pixel_blend_mode doesn't make a lot of sense for non-alpha formats but may
have a negative effect on Mike's fix
https://lore.kernel.org/dri-devel/20250627145058.6880-1-mike.looijmans@topic.nl/
if user isn't careful enough around this property.

> > +
> > + 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

Thank you,
Anatoliy