stmmac: add last_segment field to dma data

last_segment field is read twice from dma descriptors in stmmac_clean().
Add last_segment to dma data so that this flag is from priv
structure in cache instead of memory.
It avoids reading twice from memory for each loop in stmmac_clean().

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -150,8 +150,9 @@ static void stmmac_refill_desc3(void *priv_ptr, struct dma_desc *p)
 static void stmmac_clean_desc3(void *priv_ptr, struct dma_desc *p)
 {
 	struct stmmac_priv *priv = (struct stmmac_priv *)priv_ptr;
+	unsigned int entry = priv->dirty_tx;
 
-	if (priv->hw->desc->get_tx_ls(p) && !priv->extend_desc)
+	if (priv->tx_skbuff_dma[entry].last_segment && !priv->extend_desc)
 		/* NOTE: Device will overwrite des3 with timestamp value if
 		 * 1588-2002 time stamping is enabled, hence reinitialize it
 		 * to keep explicit chaining in the descriptor.

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -46,6 +46,7 @@ struct stmmac_tx_info {
 	dma_addr_t buf;
 	bool map_as_page;
 	unsigned len;
+	bool last_segment;
 };
 
 struct stmmac_priv {

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

@@ -1094,6 +1094,7 @@ static int init_dma_desc_rings(struct net_device *dev, gfp_t flags)
 		priv->tx_skbuff_dma[i].buf = 0;
 		priv->tx_skbuff_dma[i].map_as_page = false;
 		priv->tx_skbuff_dma[i].len = 0;
+		priv->tx_skbuff_dma[i].last_segment = false;
 		priv->tx_skbuff[i] = NULL;
 	}
 
@@ -1326,7 +1327,7 @@ static void stmmac_tx_clean(struct stmmac_priv *priv)
 			break;
 
 		/* Verify tx error by looking at the last segment. */
-		last = priv->hw->desc->get_tx_ls(p);
+		last = priv->tx_skbuff_dma[entry].last_segment;
 		if (likely(last)) {
 			int tx_error =
 			    priv->hw->desc->tx_status(&priv->dev->stats,
@@ -1359,6 +1360,7 @@ static void stmmac_tx_clean(struct stmmac_priv *priv)
 			priv->tx_skbuff_dma[entry].map_as_page = false;
 		}
 		priv->hw->mode->clean_desc3(priv, p);
+		priv->tx_skbuff_dma[entry].last_segment = false;
 
 		if (likely(skb != NULL)) {
 			pkts_compl++;
@@ -2028,6 +2030,7 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	/* Finalize the latest segment. */
 	priv->hw->desc->close_tx_desc(desc);
+	priv->tx_skbuff_dma[entry].last_segment = true;
 
 	wmb();
 	/* According to the coalesce parameter the IC bit for the latest