Indeed, but I don't understand why the phy in this example does not
have a compatible string?

Normally, PHYs can be enumerated on the bus, in the same way USB and
PCI devices can be enumerated. The device itself then tells you what
it is campatible with, in the same way PCI and USB does. Having a
compatible string is then detrimental, because people get it wrong,
device tree says one thing, the device itself says something else,
which do we trust? There are also boards where different series of
have populated with different pin compatible PHYs. Enumeration just
works, having a compatible would be a problem.

But, there are some PHYs which you cannot enumerate, e.g they do not
respond to MDIO while held in reset, or the silicon is buggy and has
an invalid ID. In those cases, a compatible should be listed with the
correct PHY ID.

	Andrew