RE: [PATCH 2/3] drm: zynqmp: Make the video plane primary

Klymenko, Anatoliy
2025-11-15T00:57:05Z

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: dri-devel <dri-devel-bounces@lists.freedesktop.org> On Behalf Of Sean
> Anderson
> Sent: Thursday, November 13, 2025 2:52 PM
> To: Klymenko, Anatoliy <Anatoliy.Klymenko@amd.com>; 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 2/3] drm: zynqmp: Make the video plane primary
>
> Caution: This message originated from an External Source. Use proper caution
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>
> On 11/13/25 17:45, Klymenko, Anatoliy wrote:
> > [AMD Official Use Only - AMD Internal Distribution Only]
> >
> > Hi Sean,
> >
> > Thanks a lot for the patch (and tackling the alpha issue in general)
> >
> >> -----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 2/3] drm: zynqmp: Make the video plane primary
> >>
> >> Caution: This message originated from an External Source. Use proper
> caution
> >> when opening attachments, clicking links, or responding.
> >>
> >>
> >> The zynqmp has two planes: "video" and "graphics". The video plane
> >>
> >> - Is on the bottom (zpos=0) (except when chroma keying as the master
> plane)
> >> - Supports "live" input (e.g. from an external source)
> >> - Supports RGB, YUV, and YCbCr formats, including XRGB8888
> >> - Does not support transparency, except via chroma keying (colorkey)
> >> - Must cover the entire screen (translation/resizing not supported)
> >>
> >> The graphics plane
> >>
> >> - Is on the top (zpos=1)
> >> - Supports "live" input (e.g. from an external source)
> >> - Supports RGB and YUV444 formats, but not XRGB8888
> >> - Supports transparency either via
> >> - Global alpha channel, which disables per-pixel alpha when enabled
> >> - Per-pixel alpha, which cannot be used with global alpha
> >> - Chroma keying (colorkey)
> >> - Must cover the entire screen (translation/resizing not supported)
> >>
> >> Currently the graphics plane is the primary plane. Make the video plane
> >> the primary plane:
> >>
> >> - The video plane supports XRGB8888, which is the default 24-bit
> >> colorspace for X. This results in improved performance when compared
> >> to RGB565.
> >> - The graphics plane can be used as an overlay because it has a higher
> >> z-pos and supports a per-pixel alpha channel. Unfortunately, clients
> >> like weston cannot currently take advantage of this because they
> >> expect overlay planes to support translation/resizing.
> >>
> >> One downside to this approach could be that the graphics plane has worse
> >> support for YUV and YCBCr, so it may be more difficult to compose video
> >
> > Not just more difficult but practically impossible:
> > 1. GFX (in Xilinx terminology) plane doesn't support pixel upscaling, so
> > no support for NV12, YUY2 and other common video pixel formats.
> > 2. Both planes are unscalable, this means we can only output native
> > display resolution video on the top plane, or display thick black frame
> > around the picture. We are losing GFX masking capabilities.
>
> The graphics masking capabilities are the same as they always were.
>
> > 3. We won't be able to render subtitles on top of the video.
> > Probably the only practical video player option remains here is to render
> > video to a texture and embed it into graphics composition.
>
> OK, but none of this is currently possible either because of the global
> alpha setting. So do you have a specific program in mind that plays
> video and will do it with an "underlay" plane?
>

webOS, Roku OS, just to name a few. But most importantly, AMD has quite
a few customers using "underlay" plane because of its YUV 420 capability.

> >> streams into the window of a media player. However, no existing software
> >> could rely on this because there is no way to enable the per-pixel alpha
> >> channel when the graphics plane is enabled. This makes it impossible to
> >
> > This situation is a driver bug not a fatum.
>
> And yet the driver bug provides ample evidence that no one is doing this,
> so we don't need to worry about it.
>
> --Sean
>
> > Per pixel alpha blending works
> > just fine if we disable global alpha. We just need to avoid enabling it when
> > we have alpha capable GFX plane format.
> >
> >> "carve out" an area in the graphics plane where the video plane shows
> >> through. This limitation is addressed in the next patch, but it means we
> >> do not need to worry about compatibility in this area.
> >>
> >> An alternate approach could be to pretend that the graphics plane
> >> supports XRGB8888 by using the supported ARGB8888 mode instead and
> >> enabling the global alpha channel. However, this would rule out ever
> >> using the per-pixel alpha channel.
> >>
> >> Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
> >> ---
> >>
> >> drivers/gpu/drm/xlnx/zynqmp_kms.c | 6 +++---
> >> 1 file changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/xlnx/zynqmp_kms.c
> >> b/drivers/gpu/drm/xlnx/zynqmp_kms.c
> >> index c80a2d4034f3..456ada9ac003 100644
> >> --- a/drivers/gpu/drm/xlnx/zynqmp_kms.c
> >> +++ b/drivers/gpu/drm/xlnx/zynqmp_kms.c
> >> @@ -161,8 +161,8 @@ static int zynqmp_dpsub_create_planes(struct
> >> zynqmp_dpsub *dpsub)
> >> if (!formats)
> >> return -ENOMEM;
> >>
> >> - /* Graphics layer is primary, and video layer is overlay. */
> >> - type = i == ZYNQMP_DPSUB_LAYER_VID
> >> + /* Graphics layer is overlay, and video layer is primary. */
> >> + type = i == ZYNQMP_DPSUB_LAYER_GFX
> >> ? DRM_PLANE_TYPE_OVERLAY :
> >> DRM_PLANE_TYPE_PRIMARY;
> >> ret = drm_universal_plane_init(&dpsub->drm->dev, plane, 0,
> >> &zynqmp_dpsub_plane_funcs,
> >> @@ -322,7 +322,7 @@ static const struct drm_crtc_funcs
> >> zynqmp_dpsub_crtc_funcs = {
> >>
> >> static int zynqmp_dpsub_create_crtc(struct zynqmp_dpsub *dpsub)
> >> {
> >> - struct drm_plane *plane = &dpsub->drm-
> >> >planes[ZYNQMP_DPSUB_LAYER_GFX];
> >> + struct drm_plane *plane = &dpsub->drm-
> >> >planes[ZYNQMP_DPSUB_LAYER_VID];
> >> struct drm_crtc *crtc = &dpsub->drm->crtc;
> >> int ret;
> >>
> >> --
> >> 2.35.1.1320.gc452695387.dirty
> >
> > Thank you,
> > Anatoliy

Thank you,
Anatoliy