diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 4b95c43..bbb30d8 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -1107,6 +1107,15 @@
 
 		depth = min(sdev->host->can_queue, ata_id_queue_depth(dev->id));
 		depth = min(ATA_MAX_QUEUE - 1, depth);
+
+		/*
+		 * If this device is behind a port multiplier, we have
+		 * to share the tag map between all devices on that PMP.
+		 * Set up the shared tag map here and we get automatic.
+		 */
+		if (dev->link->ap->pmp_link)
+			scsi_init_shared_tag_map(sdev->host, ATA_MAX_QUEUE - 1);
+
 		scsi_set_tag_type(sdev, MSG_SIMPLE_TAG);
 		scsi_activate_tcq(sdev, depth);
 	}
diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h
index cf4c219..1723138 100644
--- a/include/scsi/scsi_tcq.h
+++ b/include/scsi/scsi_tcq.h
@@ -140,8 +140,18 @@
  */
 static inline int scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
 {
-	shost->bqt = blk_init_tags(depth);
-	return shost->bqt ? 0 : -ENOMEM;
+	/*
+	 * If the shared tag map isn't already initialized, do it now.
+	 * This saves callers from having to check ->bqt when setting up
+	 * devices on the shared host (for libata)
+	 */
+	if (!shost->bqt) {
+		shost->bqt = blk_init_tags(depth);
+		if (!shost->bqt)
+			return -ENOMEM;
+	}
+
+	return 0;
 }
 
 /**