r8169: remove unneeded mmiowb barriers

writex() has implicit barriers, that's what makes it different from
writex_relaxed(). Therefore these calls to mmiowb() can be removed.

This patch was recently reverted due to a dependency with another
problematic patch. But because it didn't contribute to the problem
it was rebased and can be resubmitted.
Signed-off-by: NHeiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169.c

@@ -1288,13 +1288,11 @@ static u8 rtl8168d_efuse_read(struct rtl8169_private *tp, int reg_addr)
 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)
@@ -6251,8 +6249,6 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	RTL_W8(tp, TxPoll, NPQ);
 
-	mmiowb();
-
 	if (!rtl_tx_slots_avail(tp, MAX_SKB_FRAGS)) {
 		/* Avoid wrongly optimistic queue wake-up: rtl_tx thread must
 		 * not miss a ring update when it notices a stopped queue.
@@ -6597,9 +6593,7 @@ 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;