e1000e: don't generate bad checksums for tcp packets with 0 csum

When offloading transmit checksums only, the driver was not
correctly configuring the hardware to handle the case of a zero
checksum.  For UDP the correct behavior is to leave it alone, but
for tcp the checksum must be changed from 0x0000 to 0xFFFF.  The
hardware takes care of this case but only if it is told the
packet is tcp.

Signed-off-by: Dave Graham <david.graham@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/e1000e/netdev.c

@@ -3749,8 +3749,27 @@ static bool e1000_tx_csum(struct e1000_adapter *adapter, struct sk_buff *skb)
 	struct e1000_buffer *buffer_info;
 	unsigned int i;
 	u8 css;
+	u32 cmd_len = E1000_TXD_CMD_DEXT;
+
+	if (skb->ip_summed != CHECKSUM_PARTIAL)
+		return 0;
+
+	switch (skb->protocol) {
+	case __constant_htons(ETH_P_IP):
+		if (ip_hdr(skb)->protocol == IPPROTO_TCP)
+			cmd_len |= E1000_TXD_CMD_TCP;
+		break;
+	case __constant_htons(ETH_P_IPV6):
+		/* XXX not handling all IPV6 headers */
+		if (ipv6_hdr(skb)->nexthdr == IPPROTO_TCP)
+			cmd_len |= E1000_TXD_CMD_TCP;
+		break;
+	default:
+		if (unlikely(net_ratelimit()))
+			e_warn("checksum_partial proto=%x!\n", skb->protocol);
+		break;
+	}
 
-	if (skb->ip_summed == CHECKSUM_PARTIAL) {
 	css = skb_transport_offset(skb);
 
 	i = tx_ring->next_to_use;
@@ -3763,7 +3782,7 @@ static bool e1000_tx_csum(struct e1000_adapter *adapter, struct sk_buff *skb)
 				css + skb->csum_offset;
 	context_desc->upper_setup.tcp_fields.tucse = 0;
 	context_desc->tcp_seg_setup.data = 0;
-		context_desc->cmd_and_length = cpu_to_le32(E1000_TXD_CMD_DEXT);
+	context_desc->cmd_and_length = cpu_to_le32(cmd_len);
 
 	buffer_info->time_stamp = jiffies;
 	buffer_info->next_to_watch = i;
@@ -3774,9 +3793,6 @@ static bool e1000_tx_csum(struct e1000_adapter *adapter, struct sk_buff *skb)
 	tx_ring->next_to_use = i;
 
 	return 1;
-	}
-
-	return 0;
 }
 
 #define E1000_MAX_PER_TXD	8192