PCI/P2PDMA: Introduce pci_p2pdma_unmap_sg()

Add pci_p2pdma_unmap_sg() to the two places that call pci_p2pdma_map_sg().

This is a prep patch to introduce correct mappings for p2pdma transactions
that go through the root complex.

Link: https://lore.kernel.org/r/20190730163545.4915-10-logang@deltatee.com
Link: https://lore.kernel.org/r/20190812173048.9186-10-logang@deltatee.com
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

drivers/infiniband/core/rw.c

@@ -583,8 +583,10 @@ void rdma_rw_ctx_destroy(struct rdma_rw_ctx *ctx, struct ib_qp *qp, u8 port_num,
 		break;
 	}
 
-	/* P2PDMA contexts do not need to be unmapped */
-	if (!is_pci_p2pdma_page(sg_page(sg)))
+	if (is_pci_p2pdma_page(sg_page(sg)))
+		pci_p2pdma_unmap_sg(qp->pd->device->dma_device, sg,
+				    sg_cnt, dir);
+	else
 		ib_dma_unmap_sg(qp->pd->device, sg, sg_cnt, dir);
 }
 EXPORT_SYMBOL(rdma_rw_ctx_destroy);