On Sat, Dec 05, 2020 at 08:17:24PM +0100, Rasmus Villemoes wrote:
> All the buffers and registers are already set up appropriately for an
> MTU slightly above 1500, so we just need to expose this to the
> networking stack. AFAICT, there's no need to implement .ndo_change_mtu
> when the receive buffers are always set up to support the max_mtu.
>
> This fixes several warnings during boot on our mpc8309-board with an
> embedded mv88e6250 switch:
>
> mv88e6085 mdio@e0102120:10: nonfatal error -34 setting MTU 1500 on port 0
> ...
> mv88e6085 mdio@e0102120:10: nonfatal error -34 setting MTU 1500 on port 4
> ucc_geth e0102000.ethernet eth1: error -22 setting MTU to 1504 to include DSA
> overhead
>
> The last line explains what the DSA stack tries to do: achieving an MTU
> of 1500 on-the-wire requires that the master netdevice connected to
> the CPU port supports an MTU of 1500+the tagging overhead.
>
> Fixes: bfcb813203e6 ("net: dsa: configure the MTU for switch ports")
> Cc: Vladimir Oltean <vladimir.olt...@nxp.com>
> Signed-off-by: Rasmus Villemoes <rasmus.villem...@prevas.dk>
Reviewed-by: Andrew Lunn <and...@lunn.ch>
Andrew
