net: dsa: sja1105: implement cross-chip bridging operations

sja1105 uses dsa_8021q for DSA tagging, a format which is VLAN at heart
and which is compatible with cascading. A complete description of this
tagging format is in net/dsa/tag_8021q.c, but a quick summary is that
each external-facing port tags incoming frames with a unique pvid, and
this special VLAN is transmitted as tagged towards the inside of the
system, and as untagged towards the exterior. The tag encodes the switch
id and the source port index.

This means that cross-chip bridging for dsa_8021q only entails adding
the dsa_8021q pvids of one switch to the RX filter of the other
switches. Everything else falls naturally into place, as long as the
bottom-end of ports (the leaves in the tree) is comprised exclusively of
dsa_8021q-compatible (i.e. sja1105 switches). Otherwise, there would be
a chance that a front-panel switch transmits a packet tagged with a
dsa_8021q header, header which it wouldn't be able to remove, and which
would hence "leak" out.

The only use case I tested (due to lack of board availability) was when
the sja1105 switches are part of disjoint trees (however, this doesn't
change the fact that multiple sja1105 switches still need unique switch
identifiers in such a system). But in principle, even "true" single-tree
setups (with DSA links) should work just as fine, except for a small
change which I can't test: dsa_towards_port should be used instead of
dsa_upstream_port (I made the assumption that the routing port that any
sja1105 should use towards its neighbours is the CPU port. That might
not hold true in other setups).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 45 insertions, 0 deletions

diff --git a/include/linux/dsa/8021q.h b/include/linux/dsa/8021q.h
index c620d9139c28..b8daaec0896e 100644
--- a/include/linux/dsa/8021q.h
+++ b/include/linux/dsa/8021q.h
@@ -12,11 +12,33 @@ struct sk_buff;
 struct net_device;
 struct packet_type;
 
+struct dsa_8021q_crosschip_link {
+	struct list_head list;
+	int port;
+	struct dsa_switch *other_ds;
+	int other_port;
+	refcount_t refcount;
+};
+
 #if IS_ENABLED(CONFIG_NET_DSA_TAG_8021Q)
 
 int dsa_port_setup_8021q_tagging(struct dsa_switch *ds, int index,
 				 bool enabled);
 
+int dsa_8021q_crosschip_link_apply(struct dsa_switch *ds, int port,
+				   struct dsa_switch *other_ds,
+				   int other_port, bool enabled);
+
+int dsa_8021q_crosschip_bridge_join(struct dsa_switch *ds, int port,
+				    struct dsa_switch *other_ds,
+				    int other_port, struct net_device *br,
+				    struct list_head *crosschip_links);
+
+int dsa_8021q_crosschip_bridge_leave(struct dsa_switch *ds, int port,
+				     struct dsa_switch *other_ds,
+				     int other_port, struct net_device *br,
+				     struct list_head *crosschip_links);
+
 struct sk_buff *dsa_8021q_xmit(struct sk_buff *skb, struct net_device *netdev,
 			       u16 tpid, u16 tci);
 
@@ -36,6 +58,29 @@ int dsa_port_setup_8021q_tagging(struct dsa_switch *ds, int index,
 	return 0;
 }
 
+int dsa_8021q_crosschip_link_apply(struct dsa_switch *ds, int port,
+				   struct dsa_switch *other_ds,
+				   int other_port, bool enabled)
+{
+	return 0;
+}
+
+int dsa_8021q_crosschip_bridge_join(struct dsa_switch *ds, int port,
+				    struct dsa_switch *other_ds,
+				    int other_port, struct net_device *br,
+				    struct list_head *crosschip_links)
+{
+	return 0;
+}
+
+int dsa_8021q_crosschip_bridge_leave(struct dsa_switch *ds, int port,
+				     struct dsa_switch *other_ds,
+				     int other_port, struct net_device *br,
+				     struct list_head *crosschip_links)
+{
+	return 0;
+}
+
 struct sk_buff *dsa_8021q_xmit(struct sk_buff *skb, struct net_device *netdev,
 			       u16 tpid, u16 tci)
 {