[PATCH v3 7/7] [wip] virtio-gpu: add page flip support

[Gerd Hoffmann]

  Hi,

> > But I'll take you up on the implied offer to help out and test ;-)
> 
> git://people.freedesktop.org/~danvet/drm stuff

Tried that branch.

> Would be really awesome if you could test this on virtio. Note that the
> new nonblocking helpers require that your atomic backend gets the drm
> event handling right. So if there's a bug in that logic then you'll see
> lots of dmesg noise about waits timing out (after 10s of waiting). From a
> quick inspection it should work though.

No timeouts.  Yay!

But it seems crtcs can be (temporarely) disabled now, so we might have
to pick up the crtc from old_state in virtio_gpu_plane_atomic_update to
figure which virtual output needs to be turned off.  Ran into this last
week already.  Happened with multihead setups only, but the same patch
fixes this one too ;)

https://lists.freedesktop.org/archives/dri-devel/2016-May/108772.html

cheers,
  Gerd