net: dsa: sja1105: prepare tagger for handling DSA tags and VLAN simultaneously

In VLAN-unaware mode, sja1105 uses VLAN tags with a custom TPID of
0xdadb. While in the yet-to-be introduced best_effort_vlan_filtering
mode, it needs to work with normal VLAN TPID values.

A complication arises when we must transmit a VLAN-tagged packet to the
switch when it's in VLAN-aware mode. We need to construct a packet with
2 VLAN tags, and the switch will use the outer header for routing and
pop it on egress. But sadly, here the 2 hardware generations don't
behave the same:

- E/T switches won't pop an ETH_P_8021AD tag on egress, it seems
  (packets will remain double-tagged).
- P/Q/R/S switches will drop a packet with 2 ETH_P_8021Q tags (it looks
  like it tries to prevent VLAN hopping).

But looks like the reverse is also true:

- E/T switches have no problem popping the outer tag from packets with
  2 ETH_P_8021Q tags.
- P/Q/R/S will have no problem popping a single tag even if that is
  ETH_P_8021AD.

So it is clear that if we want the hardware to work with dsa_8021q
tagging in VLAN-aware mode, we need to send different TPIDs depending on
revision. Keep that information in priv->info->qinq_tpid.

The per-port tagger structure will hold an xmit_tpid value that depends
not only upon the qinq_tpid, but also upon the VLAN awareness state
itself (in case we must transmit using 0xdadb).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/net/dsa/sja1105/sja1105_main.c b/drivers/net/dsa/sja1105/sja1105_main.c
index 7b9c3db98e1d..b7e4a85caade 100644
--- a/drivers/net/dsa/sja1105/sja1105_main.c
+++ b/drivers/net/dsa/sja1105/sja1105_main.c
@@ -2153,6 +2153,15 @@ static int sja1105_vlan_filtering(struct dsa_switch *ds, int port, bool enabled)
 		tpid2 = ETH_P_SJA1105;
 	}
 
+	for (port = 0; port < ds->num_ports; port++) {
+		struct sja1105_port *sp = &priv->ports[port];
+
+		if (enabled)
+			sp->xmit_tpid = priv->info->qinq_tpid;
+		else
+			sp->xmit_tpid = ETH_P_SJA1105;
+	}
+
 	if (!enabled)
 		state = SJA1105_VLAN_UNAWARE;
 	else
@@ -2866,6 +2875,7 @@ static int sja1105_probe(struct spi_device *spi)
 			goto out;
 		}
 		skb_queue_head_init(&sp->xmit_queue);
+		sp->xmit_tpid = ETH_P_SJA1105;
 	}
 
 	return 0;