dsa: add support for original DSA tagging format

Most of the DSA switches currently in the field do not support the
Ethertype DSA tagging format that one of the previous patches added
support for, but only the original DSA tagging format.

The original DSA tagging format carries the same information as the
Ethertype DSA tagging format, but with the difference that it does not
have an ethertype field.  In other words, when receiving a packet that
is tagged with an original DSA tag, there is no way of telling in
eth_type_trans() that this packet is in fact a DSA-tagged packet.

This patch adds a hook into eth_type_trans() which is only compiled in
if support for a switch chip that doesn't support Ethertype DSA is
selected, and which checks whether there is a DSA switch driver
instance attached to this network device which uses the old tag format.
If so, it sets the protocol field to ETH_P_DSA without looking at the
packet, so that the packet ends up in the right place.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Tested-by: Nicolas Pitre <nico@marvell.com>
Tested-by: Peter van Valderen <linux@ddcrew.com>
Tested-by: Dirk Teurlings <dirk@upexia.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 647a9edee375..dae47e7a44d8 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -57,6 +57,7 @@
 #include <net/sock.h>
 #include <net/ipv6.h>
 #include <net/ip.h>
+#include <net/dsa.h>
 #include <asm/uaccess.h>
 #include <asm/system.h>
 
@@ -184,6 +185,15 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
                         skb->pkt_type = PACKET_OTHERHOST;
         }
 
+        /*
+         * Some variants of DSA tagging don't have an ethertype field
+         * at all, so we check here whether one of those tagging
+         * variants has been configured on the receiving interface,
+         * and if so, set skb->protocol without looking at the packet.
+         */
+        if (netdev_uses_dsa_tags(dev))
+                return htons(ETH_P_DSA);
+
         if (ntohs(eth->h_proto) >= 1536)
                 return eth->h_proto;