igb: Add UDP segmentation offload support

Based on a series from Alexander Duyck this change adds UDP segmentation
offload support to the igb driver.

CC: Alexander Duyck <[e-mail]>
CC: Willem de Bruijn <[e-mail]>
Signed-off-by: Josh Hunt <[e-mail]>
Tested-by: Aaron Brown <[e-mail]>
Signed-off-by: Jeff Kirsher <[e-mail]>

drivers/net/ethernet/intel/igb/e1000_82575.h

···
 };
 
 #define E1000_ADVTXD_MACLEN_SHIFT    9  /* Adv ctxt desc mac len shift */
+#define E1000_ADVTXD_TUCMD_L4T_UDP 0x00000000  /* L4 Packet TYPE of UDP */
 #define E1000_ADVTXD_TUCMD_IPV4    0x00000400  /* IP Packet Type: 1=IPv4 */
 #define E1000_ADVTXD_TUCMD_L4T_TCP 0x00000800  /* L4 Packet TYPE of TCP */
 #define E1000_ADVTXD_TUCMD_L4T_SCTP 0x00001000 /* L4 packet TYPE of SCTP */

drivers/net/ethernet/intel/igb/igb_main.c

···
 	if (unlikely(mac_hdr_len > IGB_MAX_MAC_HDR_LEN))
 		return features & ~(NETIF_F_HW_CSUM |
 				    NETIF_F_SCTP_CRC |
+				    NETIF_F_GSO_UDP_L4 |
 				    NETIF_F_HW_VLAN_CTAG_TX |
 				    NETIF_F_TSO |
 				    NETIF_F_TSO6);
···
 	if (unlikely(network_hdr_len >  IGB_MAX_NETWORK_HDR_LEN))
 		return features & ~(NETIF_F_HW_CSUM |
 				    NETIF_F_SCTP_CRC |
+				    NETIF_F_GSO_UDP_L4 |
 				    NETIF_F_TSO |
 				    NETIF_F_TSO6);
 
···
 			    NETIF_F_HW_CSUM;
 
 	if (hw->mac.type >= e1000_82576)
-		netdev->features |= NETIF_F_SCTP_CRC;
+		netdev->features |= NETIF_F_SCTP_CRC | NETIF_F_GSO_UDP_L4;
 
 	if (hw->mac.type >= e1000_i350)
 		netdev->features |= NETIF_F_HW_TC;
···
 	} ip;
 	union {
 		struct tcphdr *tcp;
+		struct udphdr *udp;
 		unsigned char *hdr;
 	} l4;
 	u32 paylen, l4_offset;
···
 	l4.hdr = skb_checksum_start(skb);
 
 	/* ADV DTYP TUCMD MKRLOC/ISCSIHEDLEN */
-	type_tucmd = E1000_ADVTXD_TUCMD_L4T_TCP;
+	type_tucmd = (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) ?
+		      E1000_ADVTXD_TUCMD_L4T_UDP : E1000_ADVTXD_TUCMD_L4T_TCP;
 
 	/* initialize outer IP header fields */
 	if (ip.v4->version == 4) {
···
 	/* determine offset of inner transport header */
 	l4_offset = l4.hdr - skb->data;
 
-	/* compute length of segmentation header */
-	*hdr_len = (l4.tcp->doff * 4) + l4_offset;
-
 	/* remove payload length from inner checksum */
 	paylen = skb->len - l4_offset;
-	csum_replace_by_diff(&l4.tcp->check, htonl(paylen));
+	if (type_tucmd & E1000_ADVTXD_TUCMD_L4T_TCP) {
+		/* compute length of segmentation header */
+		*hdr_len = (l4.tcp->doff * 4) + l4_offset;
+		csum_replace_by_diff(&l4.tcp->check,
+			(__force __wsum)htonl(paylen));
+	} else {
+		/* compute length of segmentation header */
+		*hdr_len = sizeof(*l4.udp) + l4_offset;
+		csum_replace_by_diff(&l4.udp->check,
+				     (__force __wsum)htonl(paylen));
+	}
 
 	/* update gso size and bytecount with header size */
 	first->gso_segs = skb_shinfo(skb)->gso_segs;