net: stmmac: arrange Tx tail pointer update to stmmac_flush_tx_descriptors

This patch organizes TX tail pointer update into a new function called
stmmac_flush_tx_descriptors() so that we can reuse it in stmmac_xmit(),
stmmac_tso_xmit() and up-coming XDP implementation.

Changes to v2:
 - Fix for warning: unused variable ‘desc_size’
   https://patchwork.hopto.org/static/nipa/457321/12170149/build_32bit/stderr

Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: elvinongbl

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -3518,6 +3518,28 @@ static void stmmac_tso_allocator(struct stmmac_priv *priv, dma_addr_t des,
 	}
 }
 
+static void stmmac_flush_tx_descriptors(struct stmmac_priv *priv, int queue)
+{
+	struct stmmac_tx_queue *tx_q = &priv->tx_queue[queue];
+	int desc_size;
+
+	if (likely(priv->extend_desc))
+		desc_size = sizeof(struct dma_extended_desc);
+	else if (tx_q->tbs & STMMAC_TBS_AVAIL)
+		desc_size = sizeof(struct dma_edesc);
+	else
+		desc_size = sizeof(struct dma_desc);
+
+	/* The own bit must be the latest setting done when prepare the
+	 * descriptor and then barrier is needed to make sure that
+	 * all is coherent before granting the DMA engine.
+	 */
+	wmb();
+
+	tx_q->tx_tail_addr = tx_q->dma_tx_phy + (tx_q->cur_tx * desc_size);
+	stmmac_set_tx_tail_ptr(priv, priv->ioaddr, tx_q->tx_tail_addr, queue);
+}
+
 /**
  *  stmmac_tso_xmit - Tx entry point of the driver for oversized frames (TSO)
  *  @skb : the socket buffer
@@ -3549,10 +3571,10 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct dma_desc *desc, *first, *mss_desc = NULL;
 	struct stmmac_priv *priv = netdev_priv(dev);
-	int desc_size, tmp_pay_len = 0, first_tx;
 	int nfrags = skb_shinfo(skb)->nr_frags;
 	u32 queue = skb_get_queue_mapping(skb);
 	unsigned int first_entry, tx_packets;
+	int tmp_pay_len = 0, first_tx;
 	struct stmmac_tx_queue *tx_q;
 	bool has_vlan, set_ic;
 	u8 proto_hdr_len, hdr;
@@ -3750,12 +3772,6 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 		stmmac_set_tx_owner(priv, mss_desc);
 	}
 
-	/* The own bit must be the latest setting done when prepare the
-	 * descriptor and then barrier is needed to make sure that
-	 * all is coherent before granting the DMA engine.
-	 */
-	wmb();
-
 	if (netif_msg_pktdata(priv)) {
 		pr_info("%s: curr=%d dirty=%d f=%d, e=%d, f_p=%p, nfrags %d\n",
 			__func__, tx_q->cur_tx, tx_q->dirty_tx, first_entry,
@@ -3766,13 +3782,7 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	netdev_tx_sent_queue(netdev_get_tx_queue(dev, queue), skb->len);
 
-	if (tx_q->tbs & STMMAC_TBS_AVAIL)
-		desc_size = sizeof(struct dma_edesc);
-	else
-		desc_size = sizeof(struct dma_desc);
-
-	tx_q->tx_tail_addr = tx_q->dma_tx_phy + (tx_q->cur_tx * desc_size);
-	stmmac_set_tx_tail_ptr(priv, priv->ioaddr, tx_q->tx_tail_addr, queue);
+	stmmac_flush_tx_descriptors(priv, queue);
 	stmmac_tx_timer_arm(priv, queue);
 
 	return NETDEV_TX_OK;
@@ -3802,10 +3812,10 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	int nfrags = skb_shinfo(skb)->nr_frags;
 	int gso = skb_shinfo(skb)->gso_type;
 	struct dma_edesc *tbs_desc = NULL;
-	int entry, desc_size, first_tx;
 	struct dma_desc *desc, *first;
 	struct stmmac_tx_queue *tx_q;
 	bool has_vlan, set_ic;
+	int entry, first_tx;
 	dma_addr_t des;
 
 	tx_q = &priv->tx_queue[queue];
@@ -4007,25 +4017,11 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	stmmac_set_tx_owner(priv, first);
 
-	/* The own bit must be the latest setting done when prepare the
-	 * descriptor and then barrier is needed to make sure that
-	 * all is coherent before granting the DMA engine.
-	 */
-	wmb();
-
 	netdev_tx_sent_queue(netdev_get_tx_queue(dev, queue), skb->len);
 
 	stmmac_enable_dma_transmission(priv, priv->ioaddr);
 
-	if (likely(priv->extend_desc))
-		desc_size = sizeof(struct dma_extended_desc);
-	else if (tx_q->tbs & STMMAC_TBS_AVAIL)
-		desc_size = sizeof(struct dma_edesc);
-	else
-		desc_size = sizeof(struct dma_desc);
-
-	tx_q->tx_tail_addr = tx_q->dma_tx_phy + (tx_q->cur_tx * desc_size);
-	stmmac_set_tx_tail_ptr(priv, priv->ioaddr, tx_q->tx_tail_addr, queue);
+	stmmac_flush_tx_descriptors(priv, queue);
 	stmmac_tx_timer_arm(priv, queue);
 
 	return NETDEV_TX_OK;