The ADM5120 has a built in ethernet switch. It has up to 6 external ports (5 on the SQFP package, the BGA package has an extra MII port). Also there is a special 'CPU' port which is used to send the packages to and from the CPU.
Internally the driver works with 6 VLANs. Each of the ports (including the cpu port) can be part of any of these vlans. These VLANS can be seen as the actual switches, if two ports are part of the same VLAN packets will be routed between them.
Switch matrix and the Linux driver
The setup of these vlans can be done using a switch matrix. This is a 6 by 7 matrix encoded into 6 bytes. Each of the bytes is the matrix setup for a single vlan. Each of the bits of such a byte represent one of the 6 ports or the cpu port. (It is possible to configure a switch without the cpu port in it, this will result in a ethernet switch with no cpu load at all.)
The Linux driver will allocate an ethernet device for each of the available vlans. Per default the driver will setup up the matrix such that each port has its own vlan and the cpu port is part off every vlan.
The driver has a few ioctls for configuring the matrix. The tool 'admswconfig' uses these to get and set the matrix. This is the output of the tool with the default matrix set:
# admswconfig eth0 ADM5120 switch detected with 5 ports eth0 is vlan0 vlan port0 port1 port2 port3 port4 CPU 0 1 1 1 1 1 2 1 1 3 1 1 4 1 1 #
In the following example ports 1,2,3 and 4 form a single switch and are mapped to eth0 and port 0 is mapped to eth1. This is the default hardwired in the Edimax BR6104 routers.
# admswconfig eth0 "1234c" # admswconfig eth1 "0c" # admswconfig eth2 "" # admswconfig eth3 "" # admswconfig eth4 "" # admswconfig eth0 ADM5120 switch detected with 5 ports eth0 is vlan0 vlan port0 port1 port2 port3 port4 CPU 0 1 1 1 1 1 1 1 1 2 3 4 #
The admswconfig tool can be downloaded from this page.