diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 667acd2..348cc02 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -308,9 +308,7 @@ int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 	tf->flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
 	tf->flags |= tf_flags;
 
-	if ((dev->flags & (ATA_DFLAG_PIO | ATA_DFLAG_NCQ_OFF |
-			   ATA_DFLAG_NCQ)) == ATA_DFLAG_NCQ &&
-	    likely(tag != ATA_TAG_INTERNAL)) {
+	if (ata_ncq_enabled(dev) && likely(tag != ATA_TAG_INTERNAL)) {
 		/* yay, NCQ */
 		if (!lba_48_ok(block, n_block))
 			return -ERANGE;
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 73902d3..ebb9185 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -945,29 +945,32 @@ int ata_scsi_change_queue_depth(struct scsi_device *sdev, int queue_depth)
 	struct ata_port *ap = ata_shost_to_port(sdev->host);
 	struct ata_device *dev;
 	unsigned long flags;
-	int max_depth;
 
-	if (queue_depth < 1)
+	if (queue_depth < 1 || queue_depth == sdev->queue_depth)
 		return sdev->queue_depth;
 
 	dev = ata_scsi_find_dev(ap, sdev);
 	if (!dev || !ata_dev_enabled(dev))
 		return sdev->queue_depth;
 
-	max_depth = min(sdev->host->can_queue, ata_id_queue_depth(dev->id));
-	max_depth = min(ATA_MAX_QUEUE - 1, max_depth);
-	if (queue_depth > max_depth)
-		queue_depth = max_depth;
-
-	scsi_adjust_queue_depth(sdev, MSG_SIMPLE_TAG, queue_depth);
-
+	/* NCQ enabled? */
 	spin_lock_irqsave(ap->lock, flags);
-	if (queue_depth > 1)
-		dev->flags &= ~ATA_DFLAG_NCQ_OFF;
-	else
+	dev->flags &= ~ATA_DFLAG_NCQ_OFF;
+	if (queue_depth == 1 || !ata_ncq_enabled(dev)) {
 		dev->flags |= ATA_DFLAG_NCQ_OFF;
+		queue_depth = 1;
+	}
 	spin_unlock_irqrestore(ap->lock, flags);
 
+	/* limit and apply queue depth */
+	queue_depth = min(queue_depth, sdev->host->can_queue);
+	queue_depth = min(queue_depth, ata_id_queue_depth(dev->id));
+	queue_depth = min(queue_depth, ATA_MAX_QUEUE - 1);
+
+	if (sdev->queue_depth == queue_depth)
+		return -EINVAL;
+
+	scsi_adjust_queue_depth(sdev, MSG_SIMPLE_TAG, queue_depth);
 	return queue_depth;
 }
 
@@ -1454,11 +1457,9 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
 static int ata_scmd_need_defer(struct ata_device *dev, int is_io)
 {
 	struct ata_port *ap = dev->ap;
+	int is_ncq = is_io && ata_ncq_enabled(dev);
 
-	if (!(dev->flags & ATA_DFLAG_NCQ))
-		return 0;
-
-	if (is_io) {
+	if (is_ncq) {
 		if (!ata_tag_valid(ap->active_tag))
 			return 0;
 	} else {
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 91bb8ce..4e4e365 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -1035,6 +1035,21 @@ static inline u8 ata_chk_status(struct ata_port *ap)
 	return ap->ops->check_status(ap);
 }
 
+/**
+ *	ata_ncq_enabled - Test whether NCQ is enabled
+ *	@dev: ATA device to test for
+ *
+ *	LOCKING:
+ *	spin_lock_irqsave(host lock)
+ *
+ *	RETURNS:
+ *	1 if NCQ is enabled for @dev, 0 otherwise.
+ */
+static inline int ata_ncq_enabled(struct ata_device *dev)
+{
+	return (dev->flags & (ATA_DFLAG_PIO | ATA_DFLAG_NCQ_OFF |
+			      ATA_DFLAG_NCQ)) == ATA_DFLAG_NCQ;
+}
 
 /**
  *	ata_pause - Flush writes and pause 400 nanoseconds.