Should I submit a patch to make dsa work like this then?

dsa_switch_setup() {
        ....
        ds->ops->setup()
        ....
        if (ds->ops->phy_read) {
              if (ds->slave_mii_bus)
                    error("ds->ops->phy_read is set, I should be the
one allocating ds->slave_mii_bus!")
              ...allocate and register ds->slave_mii_bus...
        }
}

You could add a WARN_ON(ds->ops->phy_read && ds->ops->phy_read);

    Andrew