[PATCH 4/6] virtio: Add helper functions to attach/detach vring descriptors

[Ying-Chun Liu (PaulLiu)]

From: Will Deacon <willdeacon at google.com>

Move the attach and detach logic for manipulating vring descriptors
out into their own functions so that we can later extend these to
bounce the data for devices with VIRTIO_F_IOMMU_PLATFORM set.

Signed-off-by: Will Deacon <willdeacon at google.com>
[ Paul: pick from the Android tree. Rebase to the upstream ]
Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu at linaro.org>
Cc: Bin Meng <bmeng.cn at gmail.com>
Link: https://android.googlesource.com/platform/external/u-boot/+/f73258a4bfe968c5f935db45f2ec5cc0104ee796
---
 drivers/virtio/virtio_ring.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 5aeb13fd59..1bd19add75 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -47,6 +47,10 @@ static unsigned int virtqueue_attach_desc(struct virtqueue *vq, unsigned int i,
 	return desc_shadow->next;
 }
 
+static void virtqueue_detach_desc(struct virtqueue *vq, unsigned int idx)
+{
+}
+
 int virtqueue_add(struct virtqueue *vq, struct virtio_sg *sgs[],
 		  unsigned int out_sgs, unsigned int in_sgs)
 {
@@ -165,10 +169,12 @@ static void detach_buf(struct virtqueue *vq, unsigned int head)
 	i = head;
 
 	while (vq->vring_desc_shadow[i].flags & VRING_DESC_F_NEXT) {
+		virtqueue_detach_desc(vq, i);
 		i = vq->vring_desc_shadow[i].next;
 		vq->num_free++;
 	}
 
+	virtqueue_detach_desc(vq, i);
 	vq->vring_desc_shadow[i].next = vq->free_head;
 	vq->free_head = head;
 
-- 
2.39.2