net: dsa: mv88e6xxx: Improve multichip isolation of standalone ports

Given that standalone ports are now configured to bypass the ATU and
forward all frames towards the upstream port, extend the ATU bypass to
multichip systems.

Load VID 0 (standalone) into the VTU with the policy bit set. Since
VID 4095 (bridged) is already loaded, we now know that all VIDs in use
are always available in all VTUs. Therefore, we can safely enable
802.1Q on DSA ports.

Setting the DSA ports' VTU policy to TRAP means that all incoming
frames on VID 0 will be classified as MGMT - as a result, the ATU is
bypassed on all subsequent switches.

With this isolation in place, we are able to support configurations
that are simultaneously very quirky and very useful. Quirky because it
involves looping cables between local switchports like in this
example:

   CPU
    |     .------.
.---0---. | .----0----.
|  sw0  | | |   sw1   |
'-1-2-3-' | '-1-2-3-4-'
  $ @ '---'   $ @ % %

We have three physically looped pairs ($, @, and %).

This is very useful because it allows us to run the kernel's
kselftests for the bridge on mv88e6xxx hardware.

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 6e5ef62a7dce..ca8c14b547b4 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -591,6 +591,12 @@ static inline bool dsa_is_upstream_port(struct dsa_switch *ds, int port)
 	return port == dsa_upstream_port(ds, port);
 }
 
+/* Return true if this is a DSA port leading away from the CPU */
+static inline bool dsa_is_downstream_port(struct dsa_switch *ds, int port)
+{
+	return dsa_is_dsa_port(ds, port) && !dsa_is_upstream_port(ds, port);
+}
+
 /* Return the local port used to reach the CPU port */
 static inline unsigned int dsa_switch_upstream_port(struct dsa_switch *ds)
 {