[PATCH] drm/virtio: Fix flickering issue seen with imported dmabufs

[Vivek Kasireddy]

We need to save the reservation object pointer associated with the
imported dmabuf in the newly created GEM object to allow
drm_gem_plane_helper_prepare_fb() to extract the exclusive fence
from it and attach it to the plane state during prepare phase.
This is needed to ensure that drm_atomic_helper_wait_for_fences()
correctly waits for the relevant fences (move, etc) associated with
the reservation object, thereby implementing proper synchronization.

Otherwise, artifacts or slight flickering can be seen when apps
are dragged across the screen when running Gnome (Wayland). This
problem is mostly seen with dGPUs in the case where the FBs are
allocated in VRAM but need to be migrated to System RAM as they
are shared with virtio-gpu.

Fixes: ca77f27a2665 ("drm/virtio: Import prime buffers from other devices as guest blobs")
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Dmitry Osipenko <dmitry.osipenko at collabora.com>
Cc: Gurchetan Singh <gurchetansingh at chromium.org>
Cc: Chia-I Wu <olvaffe at gmail.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy at intel.com>
---
 drivers/gpu/drm/virtio/virtgpu_prime.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_prime.c b/drivers/gpu/drm/virtio/virtgpu_prime.c
index fe6a0b018571..ceb0401a000b 100644
--- a/drivers/gpu/drm/virtio/virtgpu_prime.c
+++ b/drivers/gpu/drm/virtio/virtgpu_prime.c
@@ -332,6 +332,7 @@ struct drm_gem_object *virtgpu_gem_prime_import(struct drm_device *dev,
 	}
 
 	obj->import_attach = attach;
+	obj->resv = buf->resv;
 	get_dma_buf(buf);
 
 	ret = virtgpu_dma_buf_init_obj(dev, bo, attach);
-- 
2.48.1