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Date:   Tue, 30 Mar 2021 09:55:10 +0300
From:   Pekka Paalanen <ppaalanen@gmail.com>
To:     Simon Ser <contact@emersion.fr>,
        Paul Cercueil <paul@crapouillou.net>
Cc:     Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, od@zcrc.me,
        Maxime Ripard <maxime@cerno.tech>, stable@vger.kernel.org
Subject: Re: [PATCH] drm: DON'T require each CRTC to have a unique primary
 plane
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On Mon, 29 Mar 2021 15:36:27 +0000
Simon Ser <contact@emersion.fr> wrote:

> On Monday, March 29th, 2021 at 5:32 PM, Paul Cercueil <paul@crapouillou.n=
et> wrote:
>=20
> > Making the second plane an overlay would break the ABI, which is never
> > something I'm happy to do; but I'd prefer to do it now than later. =20
>=20
> Yeah, I wonder if some user-space depends on this behavior somehow?
>=20
> > I still have concerns about the user-space being "clever" enough to
> > know it can disable the primary plane. Can e.g. wlroots handle that? =20
>=20
> wlroots will always pick the first primary plane, and will never use
> overlays. The plan is to use libliftoff [1] to make use of overlay
> planes. libliftoff should already support the scenario you describe.
>=20
> I think Weston supports that too.

Weston supports overlays, but I don't think it will try without "the"
primary plane, IIRC. I'd need to verify.

I'm not quite sure what Weston would do with multiple primary planes.
It probably picks one for a CRTC ahead of time, and then sticks to it,
always using it.

But if Weston never worked with a driver to begin with, it also can't
regress, so you're safe.


Thanks,
pq

>=20
> [1]: https://github.com/emersion/libliftoff
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel


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