[PATCH wayland-protocols v7] Add zwp_linux_explicit_synchronization_v1

[Pekka Paalanen]

On Fri, 23 Nov 2018 13:07:37 +0000
Tomek Bury <tomek.bury at gmail.com> wrote:

> Hi Alexandros,
> 
> Sorry for a delay. I've finally got an end-to-end system to test it out. It
> took some time because Weston backend I wrote a while back needed serious
> rework to catch up with latest changes.
> 
> There's one thing that didn't work for me. In compositor you reject
> anything that isn't a DMA buffer and then in glrenderer you put an extra
> assertion. Why? All you do is use an EGL extension in order to import
> external fence_fd. There's no dmabuf dependency there. As long as the EGL
> implementation exposes EGL_SYNC_NATIVE_FENCE_ANDROID extension this should
> "just work" (tm) for the GL renderer. It certainly did for me. CPU-based
> renderers can poll() to wait.

Hi Tomek,

with Weston it was decided not to implement a poll() based wait at
first as implementing that properly (not blocking the compositor) would
be a big hassle and no-one could see the benefit of it given what
clients could actually produce.

Therefore the acquire fence can only apply to buffers which can be
pipelined to a GPU. Mesa EGL is using zwp_linux_dmabuf, but the support
could be extended to opaque EGL buffers very well. We just chose to
start small and bring up the infrastructure around fences first.

Restrictions on buffer types etc. can certainly be lifted in the future
if there are good use cases. I presume you have a driver stack that
relies on the opaque EGL buffers and not zwp_linux_dmabuf any time soon?

Would anyone ever use an acquire fence with wl_shm buffers? That sounds
fundamentally wrong to me as one cannot create fences to be signalled
by userspace AFAIK. Therefore buffers whose wait cannot be pipelined to
the GPU or the display device do not make much sense to me.

> The type of buffer used is an orthogonal problem. The
> EGL_WL_bind_wayland_display
> extension takes care of GL clients' buffers in GL renderer, for anything
> else the renderer needs to know how to get pixels and use whatever means to
> put those pixels on screen.

Yeah, support for opaque EGL buffers could be added, just need to think
of a good wording, since acquire fences do not make sense for all
buffer types. A compositor must be allowed to raise protocol errors for
fence+buffer combinations it cannot use, which means that clients must
know in advance what they cannot use.


Thanks,
pq

> On Tue, 13 Nov 2018 at 09:33, Tomek Bury <tomek.bury at gmail.com> wrote:
> 
> > Thanks!
> >
> > On Tue, Nov 13, 2018 at 9:08 AM Alexandros Frantzis <  
> > alexandros.frantzis at collabora.com> wrote:  
> >  
> >> On Mon, Nov 12, 2018 at 12:39:58PM +0000, Tomek Bury wrote:  
> >> > On Mon, Nov 12, 2018 at 11:15 AM Daniel Stone <daniel at fooishbar.org>  
> >> wrote:  
> >> >  
> >> > > On Fri, 9 Nov 2018 at 10:48, Pekka Paalanen <ppaalanen at gmail.com>  
> >> wrote:  
> >> > > > I can add that while pushing upstream, if there are no other changes
> >> > > > coming.
> >> > > >
> >> > > > Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> >> > > >
> >> > > > You have ensured that the C files generated from this revision build
> >> > > > fine in Weston, right?
> >> > > >
> >> > > > David, Daniel, since your name is in the maintainers, can I have  
> >> your  
> >> > > > R-b, please?  
> >> > >
> >> > > The protocol is:
> >> > > Reviewed-by: Daniel Stone <daniels at collabora.com>
> >> > >
> >> > > The Weston implementation looks pretty good so far, though there's no
> >> > > full implementation of release yet.
> >> > >
> >> > > Cheers,
> >> > > Daniel
> >> > > _______________________________________________
> >> > > wayland-devel mailing list
> >> > > wayland-devel at lists.freedesktop.org
> >> > > https://lists.freedesktop.org/mailman/listinfo/wayland-devel
> >> > >  
> >> >
> >> > HI Daniel,
> >> >
> >> > Where can I find the work-in-progress implementation? I'd like to try it
> >> > out with Broadcom driver which doesn't have implicit cross-process  
> >> sync. I  
> >> > can add the explicit sync protocol implementation on the driver side but
> >> > I'd need a reference to test it against.
> >> >
> >> > Cheers,
> >> > Tomek  
> >>
> >> Hi Tomek,
> >>
> >> the WIP implementation can be found here [1]. I hope to push an update,
> >> including some zwp_buffer_release_v1 correctness fixes, in the following
> >> days.
> >>
> >> Thanks,
> >> Alexandros
> >>
> >> [1] https://gitlab.freedesktop.org/wayland/weston/merge_requests/32
> >>  
> >  

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