Revert "r8169: remove unneeded mmiowb barriers"

This reverts commit bd7153bd.

There doesn't seem to be anything wrong with this patch,
it's just reverted to get a stable baseline again.
Signed-off-by: NHeiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169.c

@@ -1286,11 +1286,13 @@ static u16 rtl_get_events(struct rtl8169_private *tp)
 static void rtl_ack_events(struct rtl8169_private *tp, u16 bits)
 {
 	RTL_W16(tp, IntrStatus, bits);
+	mmiowb();
 }
 
 static void rtl_irq_disable(struct rtl8169_private *tp)
 {
 	RTL_W16(tp, IntrMask, 0);
+	mmiowb();
 }
 
 #define RTL_EVENT_NAPI_RX	(RxOK | RxErr)
@@ -6130,8 +6132,10 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 	if (unlikely(stop_queue))
 		netif_stop_queue(dev);
 
-	if (__netdev_sent_queue(dev, skb->len, skb->xmit_more))
+	if (__netdev_sent_queue(dev, skb->len, skb->xmit_more)) {
 		RTL_W8(tp, TxPoll, NPQ);
+		mmiowb();
+	}
 
 	if (unlikely(stop_queue)) {
 		/* Sync with rtl_tx:
@@ -6483,7 +6487,9 @@ static int rtl8169_poll(struct napi_struct *napi, int budget)
 
 	if (work_done < budget) {
 		napi_complete_done(napi, work_done);
+
 		rtl_irq_enable(tp);
+		mmiowb();
 	}
 
 	return work_done;