[SCSI] libsas: fix loopback topology bug during discovery

In some test envirenment, there is loopback topology test. We should
handle this during discovery.
Signed-off-by: Jack Wang <jack_wang@usish.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/libsas/sas_expander.c

@@ -244,6 +244,11 @@ static int sas_ex_phy_discover_helper(struct domain_device *dev, u8 *disc_req,
 		 * dev to host FIS as described in section G.5 of
 		 * sas-2 r 04b */
 		dr = &((struct smp_resp *)disc_resp)->disc;
+		if (memcmp(dev->sas_addr, dr->attached_sas_addr,
+			  SAS_ADDR_SIZE) == 0) {
+			sas_printk("Found loopback topology, just ignore it!\n");
+			return 0;
+		}
 		if (!(dr->attached_dev_type == 0 &&
 		      dr->attached_sata_dev))
 			break;