KMS to multiple displays, was Re: Building a graph for HDR10 output - stumped at sink

Bill Hofmann bill.hofmann at
Sat Apr 23 17:20:22 UTC 2022


Thanks for the details. I understand the enormity of the challenge for a
general desktop environment when you have to mix SDR and PQ-HDR (having
worked on HDR support on the Windows desktop and in the Xbox while at
Dolby). It's a nasty problem.  My goal is to *JUST* display HDR10 full
screen via HDMI to an HDR-capable TV, never displaying anything else, no
tonemapping, etc.  The additional (OPTIONAL, so prepared to punt) challenge
is to drive multiple displays with different HDR10 content. (The
alternative being having multiple SBCs/NUCs, 1 per screen, and figure out
sync one of several ways)

So, it looks like while the "correct" solution is to wait on Wayland
compositor, the two plausible approaches to a solution short term seem to

1. Punt on 1..n computer..HDR display, just bump up the system cost a bit
with 1..1 computer..display
2. Build something by hand (not using gstreamer) where the part that uses
KMS/DRM handles all n streams and displays

If that seems correct, then alas I think I know what my choice will be. :(


On Sat, Apr 23, 2022 at 5:49 AM Nicolas Dufresne <nicolas at>

> Le samedi 23 avril 2022 à 16:24 +0530, Nirbheek Chauhan a écrit :
> > On Sat, Apr 23, 2022 at 3:30 AM Nicolas Dufresne via gstreamer-devel
> > <gstreamer-devel at> wrote:
> > > Though, to get out of the toy land, kmssink would need perhap to be
> ported to
> > > use atomic API, which notably allow trying calls without affecting
> other
> > > surfaces. That would build up to the need for a shared display manager
> (also
> > > known as a compositor), specially to coordinate mode setting. Which
> mostly boils
> > > down to, why not use a proper compositor ?
> > >
> >
> > Presumably the HDR10 requirement precludes the use of a compositor? Or
> > do we now have a Linux compositor that correctly implements HDR
> > features?
> "correctly" is a vast requirement. Wayland protocol for HDR10 (and up) is
> still
> under development. Here's some lecture:
> >
> > Cheers,
> > Nirbheek

Bill Hofmann
+1 510 387-0952
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