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

[Kasireddy, Vivek]

> Subject: Re: [PATCH] drm/virtio: Fix flickering issue seen with imported
> dmabufs
> 
> On 3/25/25 23:10, Vivek Kasireddy wrote:
> > 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);
> 
> Will be better to set obj->resv before drm_gem_private_object_init()
> since it checks whether obj->resv was pre-inited. I'll change it while
> applying, thanks.
Sounds good. Thank you Dmitry!

Thanks,
Vivek
> 
> Reviewed-by: Dmitry Osipenko <dmitry.osipenko at collabora.com>
> 
> --
> Best regards,
> Dmitry