Re: [RFC PATCH v2 1/1] drm/virtio: new fence for every plane update

[Dmitry Osipenko <dmitry.osipenko@collabora.com>]

On 10/3/23 04:00, Dongwon Kim wrote:
> Having a fence linked to a virtio_gpu_framebuffer in the plane update sequence
> would cause conflict when several planes referencing the same framebuffer
> (e.g. Xorg screen covering multi-displays configured for an extended mode)
> and those planes are updated concurrently. So it is needed to allocate a
> fence for every plane state instead of the framebuffer.
> 
> The plane state for virtio-gpu, "struct virtio_gpu_plane_state" is added for
> this. This structure represents drm_plane_state and it contains the reference
> to virtio_gpu_fence, which was previously in "struct virtio_gpu_framebuffer".
> 
> "virtio_gpu_plane_duplicate_state" is added as well to create a
> virtio_gpu_plane_state on top of duplicated drm plane state.
> 
> Several drm helpers were slightly modified accordingly to use the fence in new
> plane state structure. virtio_gpu_plane_cleanup_fb was completely removed as
> dma_fence_put shouldn't be called here as it can mess up with the ref count
> of the fence. The fence should be put after the fence is signaled in
> virtio_gpu_resource_flush then released in virtio_gpu_array_add_fence while
> the next virtio message is being queued.
> 
> Also, the condition for adding fence, (plane->state->fb != new_state->fb) was
> removed since we now allocate a new fence for the new plane state even if both
> old and new planes are pointing to the same framebuffer.
> 
> v2: removed virtio_gpu_plane_duplicate_state as the existing helper,
>     drm_atomic_helper_plane_destroy_state does the same.
> 
> Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
> Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_drv.h   |  7 +++
>  drivers/gpu/drm/virtio/virtgpu_plane.c | 66 +++++++++++++++++---------
>  2 files changed, 51 insertions(+), 22 deletions(-)

Please write a guide how to test it. Are you using spice for the
multi-display viewer?

-- 
Best regards,
Dmitry