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

[Sean Anderson <sean.anderson@linux.dev>]

On 11/13/25 18:59, Klymenko, Anatoliy wrote:
> [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.

I don't believe that patch should be applied.

--Sean

>> > +
>> > +               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
>