PCI/P2PDMA: Fix missing check for dma_virt_ops

Drivers that use dma_virt_ops were meant to be rejected when testing
compatibility for P2PDMA.

This check got inadvertently dropped in one of the later versions of the
original patchset, so add it back.

Fixes: 52916982 ("PCI/P2PDMA: Support peer-to-peer memory")
Link: https://lore.kernel.org/r/20190702173544.21950-1-logang@deltatee.comSigned-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/p2pdma.c

@@ -468,6 +468,14 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
 		return -1;
 
 	for (i = 0; i < num_clients; i++) {
+		if (IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
+		    clients[i]->dma_ops == &dma_virt_ops) {
+			if (verbose)
+				dev_warn(clients[i],
+					 "cannot be used for peer-to-peer DMA because the driver makes use of dma_virt_ops\n");
+			return -1;
+		}
+
 		pci_client = find_parent_pci_dev(clients[i]);
 		if (!pci_client) {
 			if (verbose)
@@ -732,7 +740,7 @@ int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
 	 * p2pdma mappings are not compatible with devices that use
 	 * dma_virt_ops. If the upper layers do the right thing
 	 * this should never happen because it will be prevented
-	 * by the check in pci_p2pdma_add_client()
+	 * by the check in pci_p2pdma_distance_many()
 	 */
 	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
 			 dev->dma_ops == &dma_virt_ops))