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Commit d26c96c8 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Michael S. Tsirkin
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vring: Introduce vring_use_dma_api() 



This is a kludge, but no one has come up with a a better idea yet.
We'll introduce DMA API support guarded by vring_use_dma_api().
Eventually we may be able to return true on more and more systems,
and hopefully we can get rid of vring_use_dma_api() entirely some
day.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent e82becfc

drivers/virtio/virtio_ring.c

+24 −0
Original line number Diff line number Diff line
@@ -104,6 +104,30 @@ struct vring_virtqueue { 


#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)



/*

 * The interaction between virtio and a possible IOMMU is a mess.

 *

 * On most systems with virtio, physical addresses match bus addresses,

 * and it doesn't particularly matter whether we use the DMA API.

 *

 * On some systems, including Xen and any system with a physical device

 * that speaks virtio behind a physical IOMMU, we must use the DMA API

 * for virtio DMA to work at all.

 *

 * On other systems, including SPARC and PPC64, virtio-pci devices are

 * enumerated as though they are behind an IOMMU, but the virtio host

 * ignores the IOMMU, so we must either pretend that the IOMMU isn't

 * there or somehow map everything as the identity.

 *

 * For the time being, we preserve historic behavior and bypass the DMA

 * API.

 */



static bool vring_use_dma_api(struct virtio_device *vdev)

{

	return false;

}



static struct vring_desc *alloc_indirect(struct virtqueue *_vq,

					 unsigned int total_sg, gfp_t gfp)

{