If sg is already dma mapped, do not call dma_map_page() in
vring_map_one_sg().
In case of rpmsg, rpmsg uses dma_alloc_coherent() to allocate
memory to share with the remote. There is no pages setup
in dma_alloc_coherent().
In this case, we cannot convert the virtual address back to the
physical address. In this case, we can setup the sg_dma_addr to
store the DMA address, and also mark the sg is already mapped.
In the vring, we can detect if the address is already mapped
by checking the sg_dma_addr. If yes, do not call dma_map_page().
Signed-off-by: Wendy Liang <jliang@xxxxxxxxxx>
---
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 489bfc6..9793e1f 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -180,6 +180,12 @@ static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
if (!vring_use_dma_api(vq->vq.vdev))
return (dma_addr_t)sg_phys(sg);
+ /* If the sg is already mapped, return the DMA address */
+ if (sg_dma_address(sg)) {
+ sg->length = sg_dma_len(sg);
+ return sg_dma_address(sg);
+ }
+
/*
* We can't use dma_map_sg, because we don't use scatterlists in
* the way it expects (we don't guarantee that the scatterlist
--
1.9.1
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