r6040: save and restore MIER correctly in the interrupt routine

This patch saves the MIER register contents before treating
interrupts, then restores them correcty at the end of the
interrupt routine.

Signed-off-by: Joe Chou <Joe.Chou@rdc.com.tw>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/r6040.c

@@ -680,8 +680,10 @@ static irqreturn_t r6040_interrupt(int irq, void *dev_id)
 	struct net_device *dev = dev_id;
 	struct r6040_private *lp = netdev_priv(dev);
 	void __iomem *ioaddr = lp->base;
-	u16 status;
+	u16 misr, status;
 
+	/* Save MIER */
+	misr = ioread16(ioaddr + MIER);
 	/* Mask off RDC MAC interrupt */
 	iowrite16(MSK_INT, ioaddr + MIER);
 	/* Read MISR status and clear */
@@ -701,7 +703,7 @@ static irqreturn_t r6040_interrupt(int irq, void *dev_id)
 			dev->stats.rx_fifo_errors++;
 
 		/* Mask off RX interrupt */
-		iowrite16(ioread16(ioaddr + MIER) & ~RX_INTS, ioaddr + MIER);
+		misr &= ~RX_INTS;
 		netif_rx_schedule(dev, &lp->napi);
 	}
 
@@ -709,6 +711,9 @@ static irqreturn_t r6040_interrupt(int irq, void *dev_id)
 	if (status & TX_INTS)
 		r6040_tx(dev);
 
+	/* Restore RDC MAC interrupt */
+	iowrite16(misr, ioaddr + MIER);
+
 	return IRQ_HANDLED;
 }