---

yaml
---
r: 195152
b: refs/heads/master
c: ad2864d
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: f6e1e4f3e511589dd0c47d42b870501659e7195f
+refs/heads/master: ad2864d88718714d8b347b6209b07abb2ecd3a49

trunk/drivers/net/bfin_mac.c

@@ -985,6 +985,7 @@ static int bfin_mac_hard_start_xmit(struct sk_buff *skb,
 	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
@@ -1026,15 +1031,41 @@ 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);
 
 	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);