Commit 636e8adf authored by Vladimir Oltean's avatar Vladimir Oltean Committed by David S. Miller
Browse files

net: dsa: don't error out when drivers return ETH_DATA_LEN in .port_max_mtu() 



Currently, when dsa_slave_change_mtu() is called on a user port where
dev->max_mtu is 1500 (as returned by ds->ops->port_max_mtu()), the code
will stumble upon this check:

	if (new_master_mtu > mtu_limit)
		return -ERANGE;

because new_master_mtu is adjusted for the tagger overhead but mtu_limit
is not.

But it would be good if the logic went through, for example if the DSA
master really depends on an MTU adjustment to accept DSA-tagged frames.

To make the code pass through the check, we need to adjust mtu_limit for
the overhead as well, if the minimum restriction was caused by the DSA
user port's MTU (dev->max_mtu). A DSA user port MTU and a DSA master MTU
are always offset by the protocol overhead.

Currently no drivers return 1500 .port_max_mtu(), but this is only
temporary and a bug in itself - mv88e6xxx should have done that, but
since commit b9c587fe ("dsa: mv88e6xxx: Include tagger overhead when
setting MTU for DSA and CPU ports") it no longer does. This is a
preparation for fixing that.

Fixes: bfcb8132 ("net: dsa: configure the MTU for switch ports")
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: default avatarSimon Horman <simon.horman@corigine.com>
Reviewed-by: default avatarFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b830c964

net/dsa/slave.c

+5 −4
Original line number Diff line number Diff line
@@ -1933,6 +1933,7 @@ int dsa_slave_change_mtu(struct net_device *dev, int new_mtu) 
	int new_master_mtu;

	int old_master_mtu;

	int mtu_limit;

	int overhead;

	int cpu_mtu;

	int err;
@@ -1961,9 +1962,10 @@ int dsa_slave_change_mtu(struct net_device *dev, int new_mtu) 
			largest_mtu = slave_mtu;

	}



	mtu_limit = min_t(int, master->max_mtu, dev->max_mtu);

	overhead = dsa_tag_protocol_overhead(cpu_dp->tag_ops);

	mtu_limit = min_t(int, master->max_mtu, dev->max_mtu + overhead);

	old_master_mtu = master->mtu;

	new_master_mtu = largest_mtu + dsa_tag_protocol_overhead(cpu_dp->tag_ops);

	new_master_mtu = largest_mtu + overhead;

	if (new_master_mtu > mtu_limit)

		return -ERANGE;
@@ -1998,8 +2000,7 @@ int dsa_slave_change_mtu(struct net_device *dev, int new_mtu) 


out_port_failed:

	if (new_master_mtu != old_master_mtu)

		dsa_port_mtu_change(cpu_dp, old_master_mtu -

				    dsa_tag_protocol_overhead(cpu_dp->tag_ops));

		dsa_port_mtu_change(cpu_dp, old_master_mtu - overhead);

out_cpu_failed:

	if (new_master_mtu != old_master_mtu)

		dev_set_mtu(master, old_master_mtu);