sata_mv: don't issue two DMA commands concurrently

sata_mv allowed issuing two DMA commands concurrently which the
hardware allows.  Unfortunately, libata core layer isn't ready for
this yet and spews ugly warning message and malfunctions on this.
Don't allow concurrent DMA commands for now.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_mv.c

@@ -1134,30 +1134,16 @@ static int mv_qc_defer(struct ata_queued_cmd *qc)
 	if (ap->nr_active_links == 0)
 		return 0;
 
-	if (pp->pp_flags & MV_PP_FLAG_EDMA_EN) {
-		/*
-		 * The port is operating in host queuing mode (EDMA).
-		 * It can accomodate a new qc if the qc protocol
-		 * is compatible with the current host queue mode.
-		 */
-		if (pp->pp_flags & MV_PP_FLAG_NCQ_EN) {
-			/*
-			 * The host queue (EDMA) is in NCQ mode.
-			 * If the new qc is also an NCQ command,
-			 * then allow the new qc.
-			 */
-			if (qc->tf.protocol == ATA_PROT_NCQ)
-				return 0;
-		} else {
-			/*
-			 * The host queue (EDMA) is in non-NCQ, DMA mode.
-			 * If the new qc is also a non-NCQ, DMA command,
-			 * then allow the new qc.
-			 */
-			if (qc->tf.protocol == ATA_PROT_DMA)
-				return 0;
-		}
-	}
+	/*
+	 * The port is operating in host queuing mode (EDMA) with NCQ
+	 * enabled, allow multiple NCQ commands.  EDMA also allows
+	 * queueing multiple DMA commands but libata core currently
+	 * doesn't allow it.
+	 */
+	if ((pp->pp_flags & MV_PP_FLAG_EDMA_EN) &&
+	    (pp->pp_flags & MV_PP_FLAG_NCQ_EN) && ata_is_ncq(qc->tf.protocol))
+		return 0;
+
 	return ATA_DEFER_PORT;
 }