On Thu, Mar 31, 2022 at 02:53:46AM -0300, Luiz Angelo Daros de Luca wrote:

Hi Vladimir,

I think I found an issue with this patch.

quoted

At present there are two paths for changing the MTU of the DSA master.

The first is:

dsa_tree_setup
-> dsa_tree_setup_ports
   -> dsa_port_setup
      -> dsa_slave_create
         -> dsa_slave_change_mtu
            -> dev_set_mtu(master)

The first code from dsa_slave_change_mtu() is:

        if (!ds->ops->port_change_mtu)
               return -EOPNOTSUPP;

So, when the switch does not implement ds->ops->port_change_mtu, the
master MTU will never be updated. This is the case for
drivers/net/dsa/realtek/rtl8365mb.c. Before this patch,
ops->port_change_mtu was optional. We either need to turn it into a
mandatory function (even if it is a no-op that fails when mtu is
different) or change the dsa_slave_change_mtu to only return
-EOPNOTSUPP when the new slave MTU differs from current slave MTU.

Regards,

Luiz

Thanks Luiz, you are right, I've sent a revert patch here:
https://patchwork.kernel.org/project/netdevbpf/patch/20220331132854.1395040-1-vladimir.oltean@nxp.com/
My only problem with updating the MTU from dsa_master_setup() was that
it was taking rtnl_lock(), but it looks like I went too far by deleting
it entirely. I restored the old code structure, which should need no
further changes.