[PATCH] libata: turn off NCQ if queue depth is adjusted to 1

Turn off NCQ if queue depth is adjusted to 1.
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-scsi.c

@@ -889,6 +889,7 @@ 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)
@@ -904,6 +905,14 @@ int ata_scsi_change_queue_depth(struct scsi_device *sdev, int queue_depth)
 		queue_depth = max_depth;
 
 	scsi_adjust_queue_depth(sdev, MSG_SIMPLE_TAG, queue_depth);
+
+	spin_lock_irqsave(ap->lock, flags);
+	if (queue_depth > 1)
+		dev->flags &= ~ATA_DFLAG_NCQ_OFF;
+	else
+		dev->flags |= ATA_DFLAG_NCQ_OFF;
+	spin_unlock_irqrestore(ap->lock, flags);
+
 	return queue_depth;
 }
 
@@ -1293,7 +1302,8 @@ static unsigned int ata_scsi_rw_xlat(struct ata_queued_cmd *qc, const u8 *scsicm
 		 */
 		goto nothing_to_do;
 
-	if ((dev->flags & (ATA_DFLAG_PIO | ATA_DFLAG_NCQ)) == ATA_DFLAG_NCQ) {
+	if ((dev->flags & (ATA_DFLAG_PIO | ATA_DFLAG_NCQ_OFF |
+			   ATA_DFLAG_NCQ)) == ATA_DFLAG_NCQ) {
 		/* yay, NCQ */
 		if (!lba_48_ok(block, n_block))
 			goto out_of_range;

include/linux/libata.h

@@ -143,6 +143,7 @@ enum {
 	ATA_DFLAG_CFG_MASK	= (1 << 8) - 1,
 
 	ATA_DFLAG_PIO		= (1 << 8), /* device limited to PIO mode */
+	ATA_DFLAG_NCQ_OFF	= (1 << 9), /* devied limited to non-NCQ mode */
 	ATA_DFLAG_SUSPENDED	= (1 << 10), /* device suspended */
 	ATA_DFLAG_INIT_MASK	= (1 << 16) - 1,