[PATCH net v3 1/1] net: stmmac: Prevent DSA tags from breaking COE

[Romain Gantois]

Some DSA tagging protocols change the EtherType field in the MAC header
e.g.  DSA_TAG_PROTO_(DSA/EDSA/BRCM/MTK/RTL4C_A/SJA1105). On TX these tagged
frames are ignored by the checksum offload engine and IP header checker of
some stmmac cores.

On RX, the stmmac driver wrongly assumes that checksums have been computed
for these tagged packets, and sets CHECKSUM_UNNECESSARY.

Add an additional check in the stmmac TX and RX hotpaths so that COE is
deactivated for packets with ethertypes that will not trigger the COE and
IP header checks.

Fixes: 6b2c6e4a938f ("net: stmmac: propagate feature flags to vlan")
Cc: stable at vger.kernel.org
Reported-by: Richard Tresidder <rtresidd at electromag.com.au>
Link: https://lore.kernel.org/netdev/e5c6c75f-2dfa-4e50-a1fb-6bf4cdb617c2@electromag.com.au/
Reported-by: Romain Gantois <romain.gantois at bootlin.com>
Link: https://lore.kernel.org/netdev/c57283ed-6b9b-b0e6-ee12-5655c1c54495@bootlin.com/
Signed-off-by: Romain Gantois <romain.gantois at bootlin.com>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 23 ++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index a9b6b383e863..6797c944a2ac 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4371,6 +4371,19 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 	return NETDEV_TX_OK;
 }
 
+/* Check if ethertype will trigger IP
+ * header checks/COE in hardware
+ */
+static inline bool stmmac_has_ip_ethertype(struct sk_buff *skb)
+{
+	int depth = 0;
+	__be16 proto;
+
+	proto = __vlan_get_protocol(skb, eth_header_parse_protocol(skb), &depth);
+
+	return depth <= ETH_HLEN && (proto == htons(ETH_P_IP) || proto == htons(ETH_P_IPV6));
+}
+
 /**
  *  stmmac_xmit - Tx entry point of the driver
  *  @skb : the socket buffer
@@ -4435,9 +4448,13 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* DWMAC IPs can be synthesized to support tx coe only for a few tx
 	 * queues. In that case, checksum offloading for those queues that don't
 	 * support tx coe needs to fallback to software checksum calculation.
+	 *
+	 * Packets that won't trigger the COE e.g. most DSA-tagged packets will
+	 * also have to be checksummed in software.
 	 */
 	if (csum_insertion &&
-	    priv->plat->tx_queues_cfg[queue].coe_unsupported) {
+	    (priv->plat->tx_queues_cfg[queue].coe_unsupported ||
+	    !stmmac_has_ip_ethertype(skb))) {
 		if (unlikely(skb_checksum_help(skb)))
 			goto dma_map_err;
 		csum_insertion = !csum_insertion;
@@ -4997,7 +5014,7 @@ static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
 	stmmac_rx_vlan(priv->dev, skb);
 	skb->protocol = eth_type_trans(skb, priv->dev);
 
-	if (unlikely(!coe))
+	if (unlikely(!coe) || !stmmac_has_ip_ethertype(skb))
 		skb_checksum_none_assert(skb);
 	else
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
@@ -5513,7 +5530,7 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 		stmmac_rx_vlan(priv->dev, skb);
 		skb->protocol = eth_type_trans(skb, priv->dev);
 
-		if (unlikely(!coe))
+		if (unlikely(!coe) || !stmmac_has_ip_ethertype(skb))
 			skb_checksum_none_assert(skb);
 		else
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
-- 
2.43.0