diff --git a/drivers/serial/dz.c b/drivers/serial/dz.c
index c2f8677..656c342 100644
--- a/drivers/serial/dz.c
+++ b/drivers/serial/dz.c
@@ -108,37 +108,28 @@
 {
 	struct dz_port *dport = (struct dz_port *)uport;
 	unsigned short tmp, mask = 1 << dport->port.line;
-	unsigned long flags;
 
-	spin_lock_irqsave(&dport->port.lock, flags);
 	tmp = dz_in(dport, DZ_TCR);	/* read the TX flag */
 	tmp &= ~mask;			/* clear the TX flag */
 	dz_out(dport, DZ_TCR, tmp);
-	spin_unlock_irqrestore(&dport->port.lock, flags);
 }
 
 static void dz_start_tx(struct uart_port *uport)
 {
 	struct dz_port *dport = (struct dz_port *)uport;
 	unsigned short tmp, mask = 1 << dport->port.line;
-	unsigned long flags;
 
-	spin_lock_irqsave(&dport->port.lock, flags);
 	tmp = dz_in(dport, DZ_TCR);	/* read the TX flag */
 	tmp |= mask;			/* set the TX flag */
 	dz_out(dport, DZ_TCR, tmp);
-	spin_unlock_irqrestore(&dport->port.lock, flags);
 }
 
 static void dz_stop_rx(struct uart_port *uport)
 {
 	struct dz_port *dport = (struct dz_port *)uport;
-	unsigned long flags;
 
-	spin_lock_irqsave(&dport->port.lock, flags);
 	dport->cflag &= ~DZ_CREAD;
 	dz_out(dport, DZ_LPR, dport->cflag | dport->port.line);
-	spin_unlock_irqrestore(&dport->port.lock, flags);
 }
 
 static void dz_enable_ms(struct uart_port *port)
@@ -268,7 +259,9 @@
 	}
 	/* If nothing to do or stopped or hardware stopped. */
 	if (uart_circ_empty(xmit) || uart_tx_stopped(&dport->port)) {
+		spin_lock(&dport->port.lock);
 		dz_stop_tx(&dport->port);
+		spin_unlock(&dport->port.lock);
 		return;
 	}
 
@@ -285,8 +278,11 @@
 		uart_write_wakeup(&dport->port);
 
 	/* Are we are done. */
-	if (uart_circ_empty(xmit))
+	if (uart_circ_empty(xmit)) {
+		spin_lock(&dport->port.lock);
 		dz_stop_tx(&dport->port);
+		spin_unlock(&dport->port.lock);
+	}
 }
 
 /*
@@ -417,7 +413,12 @@
  */
 static void dz_shutdown(struct uart_port *uport)
 {
-	dz_stop_tx(uport);
+	struct dz_port *dport = (struct dz_port *)uport;
+	unsigned long flags;
+
+	spin_lock_irqsave(&dport->port.lock, flags);
+	dz_stop_tx(&dport->port);
+	spin_unlock_irqrestore(&dport->port.lock, flags);
 }
 
 /*