I already agreed with 'reg' being awkward in the later emails.
Wouldn't _ADR be more appropriate to specify PHY address on MDIO bus?

Also, how do you specify which MDIO bus the PHY is on. To fully
specify a PHY, you need both bits of information.

In DT, the phy-handle phandle can point to any PHY anywhere in the
system. This is particularly important when a Ethernet device has two
MDIO busses.

     Andrew