netdev - warnings from MTU setting on switch ports

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Date:   Mon, 30 Nov 2020 15:30:50 +0100
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Network Development <netdev@...r.kernel.org>
Cc:     Vladimir Oltean <vladimir.oltean@....com>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: warnings from MTU setting on switch ports

Hi,

Updating our mpc8309 board to 5.9, we're starting to get

[    0.709832] mv88e6085 mdio@...02120:10: nonfatal error -34 setting
MTU on port 0
[    0.720721] mv88e6085 mdio@...02120:10: nonfatal error -34 setting
MTU on port 1
[    0.731002] mv88e6085 mdio@...02120:10: nonfatal error -34 setting
MTU on port 2
[    0.741333] mv88e6085 mdio@...02120:10: nonfatal error -34 setting
MTU on port 3
[    0.752220] mv88e6085 mdio@...02120:10: nonfatal error -34 setting
MTU on port 4
[    0.764231] eth1: mtu greater than device maximum
[    0.769022] ucc_geth e0102000.ethernet eth1: error -22 setting MTU to
include DSA overhead

So it does say "nonfatal", but do we have to live with those warnings on
every boot going forward, or is there something that we could do to
silence it?

It's a mv88e6250 switch with cpu port connected to a ucc_geth interface;
the ucc_geth driver indeed does not implement ndo_change_mtu and has
->max_mtu set to the default of 1500.

Rasmus