How about adding CONFIG_RUST_PHYLIB to the first patch. Not
selectable, it's just a flag for Rust PHYLIB support.

We have to be careful with names. To some extent, CONFIG_PHYLIB means
the core of phylib. So it could be that CONFIG_RUST_PHYLIB means the
core of phylib written in rust? I doubt that will ever happen, but we
are setting a naming scheme here which i expect others will blindly
cut/paste. What we actually want is a symbol which represents the Rust
binding onto the phylib core. So i think it should have BINDING, or
WRAPPER or something like that in the name.

I know the rust build system is rather limited at the moment, but is
this required? Is it possible to build the rust code without the
phylib binding? Can your `RUST_PHYLIB` add phylib.rs to a Makefile
target only if it is enabled?

This is where the depends on PHYLIB should be. It is the Rust binding
on phylib which has the dependency on phylib, not the core rust code.


What i think the end state should be, once the Rust build system is
better is that in drivers/net/phy/Kconfig we have:

if PHYLIB

config RUST_PHYLIB_BINDING
    bool
    depends on RUST
    help
      Adds support needed for PHY drivers written in Rust. It provides
      a wrapper around the C phlib core.

and the Makefile when uses this to build the binding as a kernel
module.

	Andrew