The definition of ahci_start_engine() and ahci_stop_engine()

index f059467..0ff8be1 100644
@@ -205,6 +205,8 @@ static irqreturn_t ahci_interrupt (int i
 static void ahci_irq_clear(struct ata_port *ap);
 static int ahci_port_start(struct ata_port *ap);
 static void ahci_port_stop(struct ata_port *ap);
+static int ahci_start_engine(void __iomem *port_mmio);
+static int ahci_stop_engine(void __iomem *port_mmio);
 static void ahci_tf_read(struct ata_port *ap, struct ata_taskfile *tf);
 static void ahci_qc_prep(struct ata_queued_cmd *qc);
 static u8 ahci_check_status(struct ata_port *ap);

@@ -508,41 +510,64 @@ static void ahci_scr_write (struct ata_p
 	writel(val, (void __iomem *) ap->ioaddr.scr_addr + (sc_reg * 4));
 }
 
-static int ahci_stop_engine(struct ata_port *ap)
+static int ahci_stop_engine(void __iomem *port_mmio)
 {
-	void __iomem *mmio = ap->host_set->mmio_base;
-	void __iomem *port_mmio = ahci_port_base(mmio, ap->port_no);
-	int work;
 	u32 tmp;
 
 	tmp = readl(port_mmio + PORT_CMD);
+
+	/* Check if the HBA is idle */
+	if ((tmp & (PORT_CMD_START | PORT_CMD_LIST_ON)) == 0)
+		return 0;
+
+	/* Setting HBA to idle */
 	tmp &= ~PORT_CMD_START;
 	writel(tmp, port_mmio + PORT_CMD);
 
-	/* wait for engine to stop.  TODO: this could be
+	/* wait for engine to stop. This could be
 	 * as long as 500 msec
 	 */
-	work = 1000;
-	while (work-- > 0) {
-		tmp = readl(port_mmio + PORT_CMD);
-		if ((tmp & PORT_CMD_LIST_ON) == 0)
-			return 0;
-		udelay(10);
-	}
+	tmp = ata_wait_register(port_mmio + PORT_CMD,
+			        PORT_CMD_LIST_ON, PORT_CMD_LIST_ON, 1, 500);
+	if(tmp & PORT_CMD_LIST_ON)
+		return -EIO;
 
-	return -EIO;
+	return 0;
 }
 
-static void ahci_start_engine(struct ata_port *ap)
+static int ahci_start_engine(void __iomem *port_mmio)
 {
-	void __iomem *mmio = ap->host_set->mmio_base;
-	void __iomem *port_mmio = ahci_port_base(mmio, ap->port_no);
 	u32 tmp;
 
+	/*
+	 * Get current status
+	 */
 	tmp = readl(port_mmio + PORT_CMD);
+
+	/*
+	 * AHCI rev 1.1 section 10.3.1:
+	 * Software shall not set PxCMD.ST to '1' until it verifies
+	 * that PxCMD.CR is '0' and has set PxCMD.FRE to '1'
+	 */
+	if ((tmp & PORT_CMD_FIS_RX) == 0)
+		return -EPERM;
+
+	/*
+	 * wait for engine to become idle.
+	 */
+	tmp = ata_wait_register(port_mmio + PORT_CMD,
+				PORT_CMD_LIST_ON, PORT_CMD_LIST_ON, 1,500);
+	if(tmp & PORT_CMD_LIST_ON)
+		return -EBUSY;
+
+	/*
+	 * Start DMA
+	 */
 	tmp |= PORT_CMD_START;
 	writel(tmp, port_mmio + PORT_CMD);
 	readl(port_mmio + PORT_CMD); /* flush */
+
+	return 0;
 }
 
 static unsigned int ahci_dev_classify(struct ata_port *ap)