net/macb: Offset first RX buffer by two bytes

Make the ethernet frame payload word-aligned, possibly making the
memcpy into the skb a bit faster. This will be even more important
after we eliminate the copy altogether.

Also eliminate the redundant RX_OFFSET constant -- it has the same
definition and purpose as NET_IP_ALIGN.

Signed-off-by: Havard Skinnemoen <havard@skinnemoen.net>
[nicolas.ferre@atmel.com: adapt to newer kernel]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/cadence/macb.c b/drivers/net/ethernet/cadence/macb.c
index d5b52ff6d586065d672eed2d5ebd6c3cf2091dfa..c1f20b067abfa794c24f5183e4fd0a3160c48a00 100644 (file)
--- a/drivers/net/ethernet/cadence/macb.c
+++ b/drivers/net/ethernet/cadence/macb.c
@@ -33,9 +33,6 @@
 #define RX_RING_SIZE           512 /* must be power of 2 */
 #define RX_RING_BYTES          (sizeof(struct macb_dma_desc) * RX_RING_SIZE)
 
-/* Make the IP header word-aligned (the ethernet header is 14 bytes) */
-#define RX_OFFSET              2
-
 #define TX_RING_SIZE           128 /* must be power of 2 */
 #define TX_RING_BYTES          (sizeof(struct macb_dma_desc) * TX_RING_SIZE)
 
@@ -498,7 +495,7 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
 {
        unsigned int len;
        unsigned int frag;
-       unsigned int offset = 0;
+       unsigned int offset;
        struct sk_buff *skb;
        struct macb_dma_desc *desc;
 
@@ -509,7 +506,16 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
                macb_rx_ring_wrap(first_frag),
                macb_rx_ring_wrap(last_frag), len);
 
-       skb = netdev_alloc_skb(bp->dev, len + RX_OFFSET);
+       /*
+        * The ethernet header starts NET_IP_ALIGN bytes into the
+        * first buffer. Since the header is 14 bytes, this makes the
+        * payload word-aligned.
+        *
+        * Instead of calling skb_reserve(NET_IP_ALIGN), we just copy
+        * the two padding bytes into the skb so that we avoid hitting
+        * the slowpath in memcpy(), and pull them off afterwards.
+        */
+       skb = netdev_alloc_skb(bp->dev, len + NET_IP_ALIGN);
        if (!skb) {
                bp->stats.rx_dropped++;
                for (frag = first_frag; ; frag++) {
@@ -525,7 +531,8 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
                return 1;
        }
 
-       skb_reserve(skb, RX_OFFSET);
+       offset = 0;
+       len += NET_IP_ALIGN;
        skb_checksum_none_assert(skb);
        skb_put(skb, len);
 
@@ -549,10 +556,11 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
        /* Make descriptor updates visible to hardware */
        wmb();
 
+       __skb_pull(skb, NET_IP_ALIGN);
        skb->protocol = eth_type_trans(skb, bp->dev);
 
        bp->stats.rx_packets++;
-       bp->stats.rx_bytes += len;
+       bp->stats.rx_bytes += skb->len;
        netdev_vdbg(bp->dev, "received skb of length %u, csum: %08x\n",
                   skb->len, skb->csum);
        netif_receive_skb(skb);
@@ -1012,6 +1020,7 @@ static void macb_init_hw(struct macb *bp)
        __macb_set_hwaddr(bp);
 
        config = macb_mdc_clk_div(bp);
+       config |= MACB_BF(RBOF, NET_IP_ALIGN);  /* Make eth data aligned */
        config |= MACB_BIT(PAE);                /* PAuse Enable */
        config |= MACB_BIT(DRFCS);              /* Discard Rx FCS */
        config |= MACB_BIT(BIG);                /* Receive oversized frames */