Re: [RFC 2/4] virtio: Override device's DMA OPS with virtio_direct_dma_ops selectively

quoted

+
+	if (xen_domain())
+		goto skip_override;
+
+	if (virtio_has_iommu_quirk(dev))
+		set_dma_ops(dev->dev.parent, &virtio_direct_dma_ops);
+
+ skip_override:
+

I prefer normal if scoping as opposed to goto spaghetti pls.
Better yet move vring_use_dma_api here and use it.
Less of a chance something will break.

I agree about avoid pointless gotos here, but we can do things
perfectly well without either gotos or a confusing helper here
if we structure it right. E.g.:

	// suitably detailed comment here
	if (!xen_domain() &&
	    !virtio_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM))
		set_dma_ops(dev->dev.parent, &virtio_direct_dma_ops);

and while we're at it - modifying dma ops for the parent looks very
dangerous.  I don't think we can do that, as it could break iommu
setup interactions.  IFF we set a specific dma map ops it has to be
on the virtio device itself, of which we have full control.