mkresin:

Let me ask the fist and obvious question, have you tried to change the referenced line to netdev->max_mtu = 9000? Are 9k frames send over the wire with the change applied or introduces it any issues?

user3016863:

The best I can do is ping -c 10 -M do 192.168.1.XXX -s 2002 on Linux. When the value is 2003 or above, the packets are all lost.

nbd:

This datasheet appears to be wrong. I looked in other datsheets that describe the configuration registers in detail, and those indicate a limit of 2048 bytes per received frame. I tried bypassing that limit by changing the registers, but larger frames are still not received.

It can be made to work between the switch ports, not to the CPU port. See the other issue referenced above for details.