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>

1 files changed, 16 insertions, 7 deletions

diff --git a/drivers/net/ethernet/cadence/macb.c b/drivers/net/ethernet/cadence/macb.c
index d5b52ff6d586..c1f20b067abf 100644
--- 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 */