vdpa: introduce get_vq_dma_device()

This patch introduces a new method to query the dma device that is use
for a specific virtqueue.
Reviewed-by: Eli Cohen <elic@nvidia.com>
Tested-by: Eli Cohen <elic@nvidia.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230119061525.75068-3-jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/linux/vdpa.h

@@ -285,6 +285,11 @@ struct vdpa_map_file {
  *				@iova: iova to be unmapped
  *				@size: size of the area
  *				Returns integer: success (0) or error (< 0)
+ * @get_vq_dma_dev:		Get the dma device for a specific
+ *				virtqueue (optional)
+ *				@vdev: vdpa device
+ *				@idx: virtqueue index
+ *				Returns pointer to structure device or error (NULL)
  * @free:			Free resources that belongs to vDPA (optional)
  *				@vdev: vdpa device
  */
@@ -345,6 +350,7 @@ struct vdpa_config_ops {
 			 u64 iova, u64 size);
 	int (*set_group_asid)(struct vdpa_device *vdev, unsigned int group,
 			      unsigned int asid);
+	struct device *(*get_vq_dma_dev)(struct vdpa_device *vdev, u16 idx);
 
 	/* Free device resources */
 	void (*free)(struct vdpa_device *vdev);