Hi all,

I am working to implement virtgpu S3 function on Xen.

Currently on Xen, if we start a guest who enables virtgpu, and then
run "echo mem > /sys/power/state" to suspend guest. And run
"sudo xl trigger <guest id> s3resume" to resume guest. We can find that
the guest kernel comes back, but the display doesn't. It just shows a
black screen.

In response to the above phenomenon, I have found two problems.

First, if we move mouse on the black screen, guest kernel still sends a
cursor request to Qemu, but Qemu doesn't response. Because when guest
is suspending, it calls device_suspend, and then call into Qemu to call
virtio_reset->__virtio_queue_reset. In __virtio_queue_reset, it clears
all virtqueue information on Qemu end. So, after guest resumes, Qemu
can't get message from virtqueue.

Second, the reason why display can't come back is that when guest is
suspending, it calls into Qemu to call virtio_reset->virtio_gpu_gl_reset.
In virtio_gpu_gl_reset, it destroys all resources and resets renderer,
which are used for display. So after guest resumes, the display can't
come back to the status when guest is suspended.

This patch initializes virtqueue when guest is resuming to solve first
problem. And it notifies Qemu that guest is suspending to prevent Qemu
destroying resources, this is to solve second problem. And then, I can
bring the display back, and everything continues their actions after
guest resumes.

Modifications on Qemu end is:
https://lore.kernel.org/qemu-devel/20230608025655.1674357-2-Jiqian.Chen@amd.com/

Best regards,
Jiqian Chen.

Jiqian Chen (1):
  virtgpu: init vq during resume and notify qemu guest status

 drivers/gpu/drm/virtio/virtgpu_drv.c | 32 ++++++++++++++++++++++++++++
 drivers/gpu/drm/virtio/virtgpu_drv.h |  3 +++
 drivers/gpu/drm/virtio/virtgpu_kms.c | 30 ++++++++++++++++++--------
 drivers/gpu/drm/virtio/virtgpu_vq.c  | 15 +++++++++++++
 include/uapi/linux/virtio_gpu.h      |  9 ++++++++
 5 files changed, 80 insertions(+), 9 deletions(-)

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2.34.1