virtio_ring: cache whether we will use DMA API

Cache whether we will use DMA API, instead of doing the
check every time. We are going to check whether DMA API
is used more often in packed ring.

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/virtio/virtio_ring.c

@@ -86,6 +86,9 @@ struct vring_desc_state_split {
 struct vring_virtqueue {
 	struct virtqueue vq;
 
+	/* Is DMA API used? */
+	bool use_dma_api;
+
 	/* Can we use weak barriers? */
 	bool weak_barriers;
 
@@ -262,7 +265,7 @@ static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
 				   struct scatterlist *sg,
 				   enum dma_data_direction direction)
 {
-	if (!vring_use_dma_api(vq->vq.vdev))
+	if (!vq->use_dma_api)
 		return (dma_addr_t)sg_phys(sg);
 
 	/*
@@ -279,7 +282,7 @@ static dma_addr_t vring_map_single(const struct vring_virtqueue *vq,
 				   void *cpu_addr, size_t size,
 				   enum dma_data_direction direction)
 {
-	if (!vring_use_dma_api(vq->vq.vdev))
+	if (!vq->use_dma_api)
 		return (dma_addr_t)virt_to_phys(cpu_addr);
 
 	return dma_map_single(vring_dma_dev(vq),
@@ -289,7 +292,7 @@ static dma_addr_t vring_map_single(const struct vring_virtqueue *vq,
 static int vring_mapping_error(const struct vring_virtqueue *vq,
 			       dma_addr_t addr)
 {
-	if (!vring_use_dma_api(vq->vq.vdev))
+	if (!vq->use_dma_api)
 		return 0;
 
 	return dma_mapping_error(vring_dma_dev(vq), addr);
@@ -305,7 +308,7 @@ static void vring_unmap_one_split(const struct vring_virtqueue *vq,
 {
 	u16 flags;
 
-	if (!vring_use_dma_api(vq->vq.vdev))
+	if (!vq->use_dma_api)
 		return;
 
 	flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
@@ -1202,6 +1205,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	vq->broken = false;
 	vq->last_used_idx = 0;
 	vq->num_added = 0;
+	vq->use_dma_api = vring_use_dma_api(vdev);
 	list_add_tail(&vq->vq.list, &vdev->vqs);
 #ifdef DEBUG
 	vq->in_use = false;