Messages in this thread | | | Date | Wed, 15 Mar 2023 10:54:29 +0100 | From | Simon Horman <> | Subject | Re: [PATCH net 2/2] net: dsa: mv88e6xxx: fix max_mtu of 1492 on 6165, 6191, 6220, 6250, 6290 |
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On Tue, Mar 14, 2023 at 08:24:05PM +0200, Vladimir Oltean wrote: > There are 3 classes of switch families that the driver is aware of, as > far as mv88e6xxx_change_mtu() is concerned: > > - MTU configuration is available per port. Here, the > chip->info->ops->port_set_jumbo_size() method will be present. > > - MTU configuration is global to the switch. Here, the > chip->info->ops->set_max_frame_size() method will be present. > > - We don't know how to change the MTU. Here, none of the above methods > will be present. > > Switch families MV88E6165, MV88E6191, MV88E6220, MV88E6250 and MV88E6290 > fall in category 3. > > The blamed commit has adjusted the MTU for all 3 categories by EDSA_HLEN > (8 bytes), resulting in a new maximum MTU of 1492 being reported by the > driver for these switches. > > I don't have the hardware to test, but I do have a MV88E6390 switch on > which I can simulate this by commenting out its .port_set_jumbo_size > definition from mv88e6390_ops. The result is this set of messages at > probe time: > > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 1 > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 2 > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 3 > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 4 > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 5 > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 6 > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 7 > mv88e6085 d0032004.mdio-mii:10: nonfatal error -34 setting MTU to 1500 on port 8 > > It is highly implausible that there exist Ethernet switches which don't > support the standard MTU of 1500 octets, and this is what the DSA > framework says as well - the error comes from dsa_slave_create() -> > dsa_slave_change_mtu(slave_dev, ETH_DATA_LEN). > > But the error messages are alarming, and it would be good to suppress > them. > > As a consequence of this unlikeliness, we reimplement mv88e6xxx_get_max_mtu() > and mv88e6xxx_change_mtu() on switches from the 3rd category as follows: > the maximum supported MTU is 1500, and any request to set the MTU to a > value larger than that fails in dev_validate_mtu(). > > Fixes: b9c587fed61c ("dsa: mv88e6xxx: Include tagger overhead when setting MTU for DSA and CPU ports") > Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
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