From: Vladimir Oltean vladimir.oltean@nxp.com
[ Upstream commit 636e8adf7878eab3614250234341bde45537f47a ]
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 b9c587fed61c ("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: bfcb813203e6 ("net: dsa: configure the MTU for switch ports") Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Reviewed-by: Simon Horman simon.horman@corigine.com Reviewed-by: Florian Fainelli f.fainelli@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/dsa/slave.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/net/dsa/slave.c b/net/dsa/slave.c index a9fde48cffd43..5fe075bf479ec 100644 --- a/net/dsa/slave.c +++ b/net/dsa/slave.c @@ -1852,6 +1852,7 @@ 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;
@@ -1880,9 +1881,10 @@ 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;
@@ -1917,8 +1919,7 @@ 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);