sky2: transmit ring 64 bit conservation

This patch saves elements on transmit ring by only updating the upper
64 bit address when it changes. With many workloads skb's are located
in same region, so it saves space.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/sky2.c

@@ -1016,6 +1016,7 @@ static void tx_init(struct sky2_port *sky2)
 	le = get_tx_le(sky2, &sky2->tx_prod);
 	le->addr = 0;
 	le->opcode = OP_ADDR64 | HW_OWNER;
+	sky2->tx_last_upper = 0;
 }
 
 static inline struct tx_ring_info *tx_le_re(struct sky2_port *sky2,
@@ -1573,8 +1574,9 @@ static int sky2_xmit_frame(struct sk_buff *skb, struct net_device *dev)
 	struct sky2_tx_le *le = NULL;
 	struct tx_ring_info *re;
 	unsigned i, len;
-	u16 slot;
 	dma_addr_t mapping;
+	u32 upper;
+	u16 slot;
 	u16 mss;
 	u8 ctrl;
 
@@ -1593,9 +1595,11 @@ static int sky2_xmit_frame(struct sk_buff *skb, struct net_device *dev)
 		       dev->name, slot, skb->len);
 
 	/* Send high bits if needed */
-	if (sizeof(dma_addr_t) > sizeof(u32)) {
+	upper = upper_32_bits(mapping);
+	if (upper != sky2->tx_last_upper) {
 		le = get_tx_le(sky2, &slot);
-		le->addr = cpu_to_le32(upper_32_bits(mapping));
+		le->addr = cpu_to_le32(upper);
+		sky2->tx_last_upper = upper;
 		le->opcode = OP_ADDR64 | HW_OWNER;
 	}
 
@@ -1681,10 +1685,11 @@ static int sky2_xmit_frame(struct sk_buff *skb, struct net_device *dev)
 		if (pci_dma_mapping_error(hw->pdev, mapping))
 			goto mapping_unwind;
 
-		if (sizeof(dma_addr_t) > sizeof(u32)) {
+		upper = upper_32_bits(mapping);
+		if (upper != sky2->tx_last_upper) {
 			le = get_tx_le(sky2, &slot);
-			le->addr = cpu_to_le32(upper_32_bits(mapping));
-			le->ctrl = 0;
+			le->addr = cpu_to_le32(upper);
+			sky2->tx_last_upper = upper;
 			le->opcode = OP_ADDR64 | HW_OWNER;
 		}