PCI/P2PDMA: Update pci_p2pdma_distance_many() documentation

The comment describing pci_p2pdma_distance_many() still referred to
the devices being behind the same root port. This no longer applies
so reword the documentation.

Link: https://lore.kernel.org/r/20190730163545.4915-15-logang@deltatee.com
Link: https://lore.kernel.org/r/20190812173048.9186-15-logang@deltatee.comSigned-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

drivers/pci/p2pdma.c

@@ -517,15 +517,14 @@ upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client,
  * @num_clients: number of clients in the array
  * @verbose: if true, print warnings for devices when we return -1
  *
- * Returns -1 if any of the clients are not compatible (behind the same
- * root port as the provider), otherwise returns a positive number where
- * a lower number is the preferable choice. (If there's one client
- * that's the same as the provider it will return 0, which is best choice).
+ * Returns -1 if any of the clients are not compatible, otherwise returns a
+ * positive number where a lower number is the preferable choice. (If there's
+ * one client that's the same as the provider it will return 0, which is best
+ * choice).
  *
- * For now, "compatible" means the provider and the clients are all behind
- * the same PCI root port. This cuts out cases that may work but is safest
- * for the user. Future work can expand this to white-list root complexes that
- * can safely forward between each ports.
+ * "compatible" means the provider and the clients are either all behind
+ * the same PCI root port or the host bridges connected to each of the devices
+ * are listed in the 'pci_p2pdma_whitelist'.
  */
 int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
 			     int num_clients, bool verbose)