RE: [EXT] [PATCH net] net: mvpp2: Extract the correct ethtype from the skb for tx csum offload

I'm not sure that kind of ntohs() using is good for the Performance. 
htons(ETH_P_IP) is CONSTANT swapped Big/LittleEndian by COMPILER whilst the 
ntohs(vlan_get_protocol(skb)) is run-time short/byte-swap for every packet.

Yan Markman

-----Original Message-----
From: Maxime Chevallier [mailto:maxime.chevallier@bootlin.com] 
Sent: Thursday, October 04, 2018 11:03 AM
To: davem@davemloft.net
Cc: Maxime Chevallier <maxime.chevallier@bootlin.com>; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Antoine Tenart <redacted>; thomas.petazzoni@bootlin.com; gregory.clement@bootlin.com; miquel.raynal@bootlin.com; Nadav Haklai <redacted>; Stefan Chulski <redacted>; Yan Markman <redacted>; mw@semihalf.com
Subject: [EXT] [PATCH net] net: mvpp2: Extract the correct ethtype from the skb for tx csum offload

External Email

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When offloading the L3 and L4 csum computation on TX, we need to extract the l3_proto from the ethtype, independently of the presence of a vlan tag.

The actual driver uses skb->protocol as-is, resulting in packets with the wrong L4 checksum being sent when there's a vlan tag in the packet header and checksum offloading is enabled.

This commit makes use of vlan_protocol_get() to get the correct ethtype regardless the presence of a vlan tag.

Fixes: 3f51850 ("ethernet: Add new driver for Marvell Armada 375 network unit")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
 drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index 38cc01beea79..4bd5b251e3c7 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c

@@ -1737,7 +1737,7 @@ static u32 mvpp2_txq_desc_csum(int l3_offs, int l3_proto,
 	command |= (ip_hdr_len << MVPP2_TXD_IP_HLEN_SHIFT);
 	command |= MVPP2_TXD_IP_CSUM_DISABLE;
 
-	if (l3_proto == htons(ETH_P_IP)) {
+	if (l3_proto == ETH_P_IP) {
 		command &= ~MVPP2_TXD_IP_CSUM_DISABLE;	/* enable IPv4 csum */
 		command &= ~MVPP2_TXD_L3_IP6;		/* enable IPv4 */
 	} else {

@@ -2600,14 +2600,15 @@ static u32 mvpp2_skb_tx_csum(struct mvpp2_port *port, struct sk_buff *skb)
 	if (skb->ip_summed == CHECKSUM_PARTIAL) {
 		int ip_hdr_len = 0;
 		u8 l4_proto;
+		int l3_proto = ntohs(vlan_get_protocol(skb));
 
-		if (skb->protocol == htons(ETH_P_IP)) {
+		if (l3_proto == ETH_P_IP) {
 			struct iphdr *ip4h = ip_hdr(skb);
 
 			/* Calculate IPv4 checksum and L4 checksum */
 			ip_hdr_len = ip4h->ihl;
 			l4_proto = ip4h->protocol;
-		} else if (skb->protocol == htons(ETH_P_IPV6)) {
+		} else if (l3_proto == ETH_P_IPV6) {
 			struct ipv6hdr *ip6h = ipv6_hdr(skb);
 
 			/* Read l4_protocol from one of IPv6 extra headers */ @@ -2619,7 +2620,7 @@ static u32 mvpp2_skb_tx_csum(struct mvpp2_port *port, struct sk_buff *skb)
 		}
 
 		return mvpp2_txq_desc_csum(skb_network_offset(skb),
-				skb->protocol, ip_hdr_len, l4_proto);
+					   l3_proto, ip_hdr_len, l4_proto);
 	}
 
 	return MVPP2_TXD_L4_CSUM_NOT | MVPP2_TXD_IP_CSUM_DISABLE;
--

2.11.0