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

[Dmitry Osipenko]

On 3/26/25 08:13, Kasireddy, Vivek wrote:
>> 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!

Applied to misc-fixes, thanks!

Will keep an eye on the patch status in the misc. Too early to apply now
to misc-fixes, I rushed a bit by accident.

-- 
Best regards,
Dmitry