MLK-20780 virtio_ring: check dma_mem for xen_domain

on i.MX8QM, M4_1 is communicating with DomU using rpmsg with a fixed
address as the dma mem buffer which is predefined.

Without this patch, the flow is:
vring_map_one_sg -> vring_use_dma_api
                 -> dma_map_page
		       -> __swiotlb_map_page
		                ->swiotlb_map_page
				->__dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
However we are using per device dma area for rpmsg, phys_to_virt
could not return a correct virtual address for virtual address in
vmalloc area. Then kernel panic.

With this patch, vring_use_dma_api will return false, and
vring_map_one_sg will return sg_phys(sg) which is the correct phys
address in the predefined memory region.
vring_map_one_sg -> vring_use_dma_api
                 -> sg_phys(sg)

Signed-off-by: Peng Fan <peng.fan@nxp.com>
(cherry picked from commit 484db6e6eb6b8d0ba2cfa946caa53616e23c0364)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 9529e28..999d3c7 100644 (file)
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -143,6 +143,8 @@ struct vring_virtqueue {
 
 static bool vring_use_dma_api(struct virtio_device *vdev)
 {
+       struct device *dma_dev = vdev->dev.parent;
+
        if (!virtio_has_iommu_quirk(vdev))
                return true;
 
@@ -155,7 +157,7 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
         * the DMA API if we're a Xen guest, which at least allows
         * all of the sensible Xen configurations to work correctly.
         */
-       if (xen_domain())
+       if (xen_domain() && !dma_dev->dma_mem)
                return true;
 
        return false;