net: macb: initialize checksum when using checksum offloading

I'm still struggling to get this fix right..

Changes since v2:
 - do not blindly modify SKB contents according to Dave's legitimate
   objection

Changes since v1:
 - dropped disabling HW checksum offload for Zynq
 - initialize checksum similar to net/ethernet/freescale/fec_main.c

-- >8 --
MACB/GEM needs the checksum field initialized to 0 to get correct
results on transmit in all cases, e.g. on Zynq, UDP packets with
payload <= 2 otherwise contain a wrong checksums.

Signed-off-by: Helmut Buchsbaum <helmut.buchsbaum@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 89c0cfa9719f345cd219a096223285a89fbf88fb..d954a97b0b0b011de07ded9e69f46b893517dde1 100644 (file)
--- a/drivers/net/ethernet/cadence/macb.c
+++ b/drivers/net/ethernet/cadence/macb.c
@@ -1323,6 +1323,24 @@ dma_error:
        return 0;
 }
 
+static inline int macb_clear_csum(struct sk_buff *skb)
+{
+       /* no change for packets without checksum offloading */
+       if (skb->ip_summed != CHECKSUM_PARTIAL)
+               return 0;
+
+       /* make sure we can modify the header */
+       if (unlikely(skb_cow_head(skb, 0)))
+               return -1;
+
+       /* initialize checksum field
+        * This is required - at least for Zynq, which otherwise calculates
+        * wrong UDP header checksums for UDP packets with UDP data len <=2
+        */
+       *(__sum16 *)(skb_checksum_start(skb) + skb->csum_offset) = 0;
+       return 0;
+}
+
 static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
        u16 queue_index = skb_get_queue_mapping(skb);
@@ -1362,6 +1380,11 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
                return NETDEV_TX_BUSY;
        }
 
+       if (macb_clear_csum(skb)) {
+               dev_kfree_skb_any(skb);
+               return NETDEV_TX_OK;
+       }
+
        /* Map socket buffer for DMA transfer */
        if (!macb_tx_map(bp, queue, skb)) {
                dev_kfree_skb_any(skb);