From TI am335x Reference Manual:

14.3.2.10.2 Dual Mac Mode

When operating in dual mac mode the intention is to transfer packets
between ports 0 and 1 and ports 0 and 2, but not between ports 1 and 2.

Each CPGMAC_SL appears as a single MAC with no bridging between MAC’s.
Each CPGMAC_SL has at least one unique (not the same) mac address.

Dual mac mode is configured as described below:

- Set the ale_vlan_aware bit in the ALE_Control register. This bit
configures the ALE to process in vlan aware mode.

With X can be Port 1 or Port 2:

- Configure the Port X to Port 0 VLAN.
Add a VLAN Table Entry with ports 0 and X as members (clear the flood
masks).

Add a VLAN/Unicast Address Table Entry with the PortX/0 VLAN and
a port number of 0.

- Select the dual mac mode on the port 0 FIFO by setting
tx_in_sel[1:0] = 01 in P0_Tx_In_Ctl.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>