r8169: improve rtl8169_start_xmit

Only call rtl8169_xmit_frags() if the skb is actually fragmented.
This avoid a small overhead for non-fragmented skb's, and it allows
to simplify rtl8169_xmit_frags() a little.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169_main.c

@@ -4087,12 +4087,10 @@ static int rtl8169_xmit_frags(struct rtl8169_private *tp, struct sk_buff *skb,
 		tp->tx_skb[entry].len = len;
 	}
 
-	if (cur_frag) {
-		tp->tx_skb[entry].skb = skb;
-		txd->opts1 |= cpu_to_le32(LastFrag);
-	}
+	tp->tx_skb[entry].skb = skb;
+	txd->opts1 |= cpu_to_le32(LastFrag);
 
-	return cur_frag;
+	return 0;
 
 err_out:
 	rtl8169_tx_clear_range(tp, tp->cur_tx + 1, cur_frag);
@@ -4217,6 +4215,7 @@ static void rtl8169_doorbell(struct rtl8169_private *tp)
 static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 				      struct net_device *dev)
 {
+	unsigned int frags = skb_shinfo(skb)->nr_frags;
 	struct rtl8169_private *tp = netdev_priv(dev);
 	unsigned int entry = tp->cur_tx % NUM_TX_DESC;
 	struct TxDesc *txd = tp->TxDescArray + entry;
@@ -4225,9 +4224,8 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 	u32 opts[2], len;
 	bool stop_queue;
 	bool door_bell;
-	int frags;
 
-	if (unlikely(!rtl_tx_slots_avail(tp, skb_shinfo(skb)->nr_frags))) {
+	if (unlikely(!rtl_tx_slots_avail(tp, frags))) {
 		netif_err(tp, drv, dev, "BUG! Tx Ring full when queue awake!\n");
 		goto err_stop_0;
 	}
@@ -4256,14 +4254,13 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 	tp->tx_skb[entry].len = len;
 	txd->addr = cpu_to_le64(mapping);
 
-	frags = rtl8169_xmit_frags(tp, skb, opts);
-	if (frags < 0)
-		goto err_dma_1;
-	else if (frags)
-		opts[0] |= FirstFrag;
-	else {
+	if (!frags) {
 		opts[0] |= FirstFrag | LastFrag;
 		tp->tx_skb[entry].skb = skb;
+	} else {
+		if (rtl8169_xmit_frags(tp, skb, opts))
+			goto err_dma_1;
+		opts[0] |= FirstFrag;
 	}
 
 	txd->opts2 = cpu_to_le32(opts[1]);