> I want to write a driver to control my PHY device.

Ethernet PHYs are quite literally (through
the MDIO bus) tied to their ethernet nic.

As such, the same driver that controls and
configures the ethernet nic generally controls 
and configures the ethernet phy.

There are many, many examples of ethernet
drivers (both 6.3 io-net and 6.4 io-pkt) 
which do this.

Generally, it is best to look over the source,
and find a driver which is closest to your
hardware, and use it as a starting point.

I still don't recommend the alien green women,
though, no matter how much Captain Kirk was
fond of them.

--
aboyd