[RFC v1 0/4] drm: Add support for DRM_CAP_DEFERRED_OUT_FENCE capability

[Gerd Hoffmann]

  Hi,

> - We fix virtio to send out the completion event at the end of this entire
>   pipeline, i.e. virtio code needs to take care of sending out the
>   crtc_state->event correctly.

That sounds sensible to me.  Fence the virtio commands, make sure (on
the host side) the command completes only when the work is actually done
not only submitted.  Has recently been added to qemu for RESOURCE_FLUSH
(aka frontbuffer rendering) and doing the same for SET_SCANOUT (aka
pageflipping), then send vblank events to userspace on command
completion certainly makes sense.

take care,
  Gerd