Compile errors when building v1.0.30tux2 (Gentoo)

Ahoy, TUXEDO Computers. I have been trying for about a week to get all your software up and operational on my new InfinityBook, under Gentoo. So far, everything is going relatively smoothly. I have a stack of notes and a guide on what I had to do, along with a few contributions, shall surely come out of it in the end.

At the moment, however, I'm stuck trying to compile the yt6801 ethernet drivers as a Kernel module and I actually don't see how they ever do compile at all. (Linux 6.16.0 with the usual Gentoo kernel patches, GCC 14.3.0)

The most obvious error is that the build is trying to compile line 342 of fuxi-gmac-phy.c and expansion is an undefined symbol. Which is true. It is. (Superficial perusal of the code suggests that it should be pdata->expansion but I'm short of time so I haven't tried patching it, yet.)

Maybe I should be defining some preprocessor symbols that stop that branch of the code being compiled? If so: I can't find them in any of the other files in the repo so I'm not sure how the Debian build passes, here, at all. (I really don't know a whole lot about Debian, though, being more of a Gentoo & Arch expert.)

(Just let me know if that's the solve and I'll move on and make sure to include it in any kind of guide or report that I write in the end.)

It could also be the case that my Kernel is missing something. I briefly traversed the included kernel headers but I didn't see anything obvious. If there's a super-obscure kernel config that needs to be set: again, please let me know.

I'm happy to say that, except for this build error, making a Gentoo .ebuild seems very realistic.