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

Sean Anderson
2025-11-13T23:07:18Z

On 11/13/25 18:03, Klymenko, Anatoliy wrote:
> [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.

Do you have a datasheet (or other) reference?

But in any case, DRM_MODE_BLEND_PREMULTI is mandatory even if we don't support
it. See drm_plane_create_blend_mode_property for details.

--Sean