1 files changed, 33 insertions, 2 deletions

diff --git a/drivers/net/bfin_mac.c b/drivers/net/bfin_mac.c
index 2b364ba6b62e..9e010d69f34a 100644
--- a/drivers/net/bfin_mac.c
+++ b/drivers/net/bfin_mac.c
@@ -985,6 +985,7 @@ out:
         return NETDEV_TX_OK;
 }
 
+#define IP_HEADER_OFF  0
 #define RX_ERROR_MASK (RX_LONG | RX_ALIGN | RX_CRC | RX_LEN | \
         RX_FRAG | RX_ADDR | RX_DMAO | RX_PHY | RX_LATE | RX_RANGE)
 
@@ -993,6 +994,10 @@ static void bfin_mac_rx(struct net_device *dev)
         struct sk_buff *skb, *new_skb;
         unsigned short len;
         struct bfin_mac_local *lp __maybe_unused = netdev_priv(dev);
+#if defined(BFIN_MAC_CSUM_OFFLOAD)
+        unsigned int i;
+        unsigned char fcs[ETH_FCS_LEN + 1];
+#endif
 
         /* check if frame status word reports an error condition
          * we which case we simply drop the packet
@@ -1026,6 +1031,8 @@ static void bfin_mac_rx(struct net_device *dev)
         current_rx_ptr->desc_a.start_addr = (unsigned long)new_skb->data - 2;
 
         len = (unsigned short)((current_rx_ptr->status.status_word) & RX_FRLEN);
+        /* Deduce Ethernet FCS length from Ethernet payload length */
+        len -= ETH_FCS_LEN;
         skb_put(skb, len);
 
         skb->protocol = eth_type_trans(skb, dev);
@@ -1033,8 +1040,32 @@ static void bfin_mac_rx(struct net_device *dev)
         bfin_rx_hwtstamp(dev, skb);
 
 #if defined(BFIN_MAC_CSUM_OFFLOAD)
-        skb->csum = current_rx_ptr->status.ip_payload_csum;
-        skb->ip_summed = CHECKSUM_COMPLETE;
+        /* Checksum offloading only works for IPv4 packets with the standard IP header
+         * length of 20 bytes, because the blackfin MAC checksum calculation is
+         * based on that assumption. We must NOT use the calculated checksum if our
+         * IP version or header break that assumption.
+         */
+        if (skb->data[IP_HEADER_OFF] == 0x45) {
+                skb->csum = current_rx_ptr->status.ip_payload_csum;
+                /*
+                 * Deduce Ethernet FCS from hardware generated IP payload checksum.
+                 * IP checksum is based on 16-bit one's complement algorithm.
+                 * To deduce a value from checksum is equal to add its inversion.
+                 * If the IP payload len is odd, the inversed FCS should also
+                 * begin from odd address and leave first byte zero.
+                 */
+                if (skb->len % 2) {
+                        fcs[0] = 0;
+                        for (i = 0; i < ETH_FCS_LEN; i++)
+                                fcs[i + 1] = ~skb->data[skb->len + i];
+                        skb->csum = csum_partial(fcs, ETH_FCS_LEN + 1, skb->csum);
+                } else {
+                        for (i = 0; i < ETH_FCS_LEN; i++)
+                                fcs[i] = ~skb->data[skb->len + i];
+                        skb->csum = csum_partial(fcs, ETH_FCS_LEN, skb->csum);
+                }
+                skb->ip_summed = CHECKSUM_COMPLETE;
+        }
 #endif
 
         netif_rx(skb);