quoted

Vladimir indicates here that it is not known how to change the max MTU
for the MV88E6250. Where did you get the information from to implement
it?

Please refer to [1].

The mv88e6185_g1_set_max_frame_size() function can be reused (as
registers' offsets and bits are the same for mv88e60{71|20}).

So you have the datasheet? You get the information to implement this
from the data sheet?

     Andrew