From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wendy Liang Subject: [PATCH 1/2] virtio_ring: Do not call dma_map_page if sg is already mapped. Date: Wed, 7 Dec 2016 22:59:12 -0800 Message-ID: <1481180353-11139-2-git-send-email-jliang@xilinx.com> References: <1481180353-11139-1-git-send-email-jliang@xilinx.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1481180353-11139-1-git-send-email-jliang@xilinx.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: jasowang@redhat.com, mst@redhat.com, virtualization@lists.linux-foundation.org, ohad@wizery.com, bjorn.andersson@linaro.org, linux-remoteproc@vger.kernel.org Cc: Wendy Liang List-Id: virtualization@lists.linuxfoundation.org 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 --- 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