gianfar: Map head TxBD first

Move the mapping of the head BD before the mapping of fragments.
The TOE (h/w offload) decision logic block can be also moved up
(as the TOE flag belongs to the head BD), resulting in more
localized code (TOE logic vs BD mapping code blocks).
Note that, for this h/w, the R (status) bit for the head BD of a S/G
frame needs to be written last for a reliable transmission.
For the fragmented skb case, a local variable is used to temporarily
store the status info of the first BD, replacing a BD status read.
A merge of 2 "if(do_tstamp)" blocks was also possible.

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/gianfar.c

@@ -2389,6 +2389,47 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	txbdp = txbdp_start = tx_queue->cur_tx;
 	lstatus = be32_to_cpu(txbdp->lstatus);
 
+	/* Add TxPAL between FCB and frame if required */
+	if (unlikely(do_tstamp)) {
+		skb_push(skb, GMAC_TXPAL_LEN);
+		memset(skb->data, 0, GMAC_TXPAL_LEN);
+	}
+
+	/* Add TxFCB if required */
+	if (fcb_len) {
+		fcb = gfar_add_fcb(skb);
+		lstatus |= BD_LFLAG(TXBD_TOE);
+	}
+
+	/* Set up checksumming */
+	if (do_csum) {
+		gfar_tx_checksum(skb, fcb, fcb_len);
+
+		if (unlikely(gfar_csum_errata_12(priv, (unsigned long)fcb)) ||
+		    unlikely(gfar_csum_errata_76(priv, skb->len))) {
+			__skb_pull(skb, GMAC_FCB_LEN);
+			skb_checksum_help(skb);
+			if (do_vlan || do_tstamp) {
+				/* put back a new fcb for vlan/tstamp TOE */
+				fcb = gfar_add_fcb(skb);
+			} else {
+				/* Tx TOE not used */
+				lstatus &= ~(BD_LFLAG(TXBD_TOE));
+				fcb = NULL;
+			}
+		}
+	}
+
+	if (do_vlan)
+		gfar_tx_vlan(skb, fcb);
+
+	bufaddr = dma_map_single(priv->dev, skb->data, skb_headlen(skb),
+				 DMA_TO_DEVICE);
+	if (unlikely(dma_mapping_error(priv->dev, bufaddr)))
+		goto dma_map_err;
+
+	txbdp_start->bufPtr = cpu_to_be32(bufaddr);
+
 	/* Time stamp insertion requires one additional TxBD */
 	if (unlikely(do_tstamp))
 		txbdp_tstamp = txbdp = next_txbd(txbdp, base,
@@ -2404,6 +2445,8 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
 			lstatus |= BD_LFLAG(TXBD_LAST | TXBD_INTERRUPT);
 		}
 	} else {
+		u32 lstatus_start = lstatus;
+
 		/* Place the fragment addresses and lengths into the TxBDs */
 		for (i = 0; i < nr_frags; i++) {
 			unsigned int frag_len;
@@ -2432,56 +2475,9 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
 			txbdp->lstatus = cpu_to_be32(lstatus);
 		}
 
-		lstatus = be32_to_cpu(txbdp_start->lstatus);
+		lstatus = lstatus_start;
 	}
 
-	/* Add TxPAL between FCB and frame if required */
-	if (unlikely(do_tstamp)) {
-		skb_push(skb, GMAC_TXPAL_LEN);
-		memset(skb->data, 0, GMAC_TXPAL_LEN);
-	}
-
-	/* Add TxFCB if required */
-	if (fcb_len) {
-		fcb = gfar_add_fcb(skb);
-		lstatus |= BD_LFLAG(TXBD_TOE);
-	}
-
-	/* Set up checksumming */
-	if (do_csum) {
-		gfar_tx_checksum(skb, fcb, fcb_len);
-
-		if (unlikely(gfar_csum_errata_12(priv, (unsigned long)fcb)) ||
-		    unlikely(gfar_csum_errata_76(priv, skb->len))) {
-			__skb_pull(skb, GMAC_FCB_LEN);
-			skb_checksum_help(skb);
-			if (do_vlan || do_tstamp) {
-				/* put back a new fcb for vlan/tstamp TOE */
-				fcb = gfar_add_fcb(skb);
-			} else {
-				/* Tx TOE not used */
-				lstatus &= ~(BD_LFLAG(TXBD_TOE));
-				fcb = NULL;
-			}
-		}
-	}
-
-	if (do_vlan)
-		gfar_tx_vlan(skb, fcb);
-
-	/* Setup tx hardware time stamping if requested */
-	if (unlikely(do_tstamp)) {
-		skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
-		fcb->ptp = 1;
-	}
-
-	bufaddr = dma_map_single(priv->dev, skb->data, skb_headlen(skb),
-				 DMA_TO_DEVICE);
-	if (unlikely(dma_mapping_error(priv->dev, bufaddr)))
-		goto dma_map_err;
-
-	txbdp_start->bufPtr = cpu_to_be32(bufaddr);
-
 	/* If time stamping is requested one additional TxBD must be set up. The
 	 * first TxBD points to the FCB and must have a data length of
 	 * GMAC_FCB_LEN. The second TxBD points to the actual frame data with
@@ -2498,6 +2494,10 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		txbdp_tstamp->bufPtr = cpu_to_be32(bufaddr);
 		txbdp_tstamp->lstatus = cpu_to_be32(lstatus_ts);
 		lstatus |= BD_LFLAG(TXBD_CRC | TXBD_READY) | GMAC_FCB_LEN;
+
+		/* Setup tx hardware time stamping */
+		skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
+		fcb->ptp = 1;
 	} else {
 		lstatus |= BD_LFLAG(TXBD_CRC | TXBD_READY) | skb_headlen(skb);
 	}