On Wed, Dec 07, 2016 at 10:59:12PM -0800, Wendy Liang wrote:
> 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 <[email protected]>
> ---
> 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 */
How come we even reach this code for rpmsg?
Does vring_use_dma_api return true for rpmsg?
> + if (sg_dma_address(sg)) {
> + sg->length = sg_dma_len(sg);
> + return sg_dma_address(sg);
> + }
> +
Is there a rule that says 0 is not a valid address?
> /*
> * 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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