Hi Gerd,

quoted

quoted

You don't have to use the rendering pipeline.  You can let the i915
gpu render into a dma-buf shared with virtio-gpu, then use
virtio-gpu only for buffer sharing with the host.

[Kasireddy, Vivek] Just to confirm my understanding of what you are suggesting, are
you saying that we need to either have Weston allocate scanout buffers (GBM surface/BO)
using virtio-gpu and render into them using i915; or have virtio-gpu allocate pages and 
export a dma-buf and have Weston create a GBM BO by calling gbm_bo_import(fd) and
render into the BO using i915?

Hmm, why a big mode switch?  You should be able to do that without modifying the
virtio-gpu guest driver.  On the host side qemu needs some work to support the most
recent virtio-gpu features like the buffer uuids (assuming you use qemu userspace), right
now those are only supported by crosvm.

[Kasireddy, Vivek] We are only interested in Qemu UI at the moment but if we were to use
virtio-gpu, we are going to need to add one more vq and support for managing buffers, 
events, etc.

Thanks,
Vivek

It might be useful to add support for display-less virtio-gpu, i.e.
"qemu -device virtio-gpu-pci,max_outputs=0".  Right now the linux driver throws an error
in case no output (crtc) is present.  Should be fixable without too much effort though,
effectively the sanity check would have to be moved from driver initialization to
commands like SET_SCANOUT which manage the outputs.

take care,
  Gerd