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| H A D | slave.c | diff 636e8adf7878eab3614250234341bde45537f47a Tue Mar 14 13:24:04 CDT 2023 Vladimir Oltean <vladimir.oltean@nxp.com> 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 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>
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