[RFC PATCH 3/3] drm/virtio: drm_gem_plane_helper_prepare_fb for obj synchronization

[Dmitry Osipenko]

On 7/13/23 01:44, Dongwon Kim wrote:
> This helper is needed for framebuffer synchronization. Old framebuffer data
> is often displayed on the guest display without this helper.
> 
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Vivek Kasireddy <vivek.kasireddy at intel.com>
> Signed-off-by: Dongwon Kim <dongwon.kim at intel.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_plane.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c
> index a063f06ab6c5..e197299489ce 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_plane.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
> @@ -26,6 +26,7 @@
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_damage_helper.h>
>  #include <drm/drm_fourcc.h>
> +#include <drm/drm_gem_atomic_helper.h>
>  
>  #include "virtgpu_drv.h"
>  
> @@ -271,6 +272,9 @@ static int virtio_gpu_plane_prepare_fb(struct drm_plane *plane,
>  	vgfb = to_virtio_gpu_framebuffer(new_state->fb);
>  	vgplane_st = to_virtio_gpu_plane_state(new_state);
>  	bo = gem_to_virtio_gpu_obj(vgfb->base.obj[0]);
> +
> +	drm_gem_plane_helper_prepare_fb(plane, new_state);

The implicit display BO sync should happen on a host side, unless you're
rendering with Venus and then displaying with virgl. Doing it on guest
side should be a major performance hit. Please provide a complete
description of your setup: what VMM you use, config options, what tests
you're running.

-- 
Best regards,
Dmitry