I'd like to add a mode where a specific driver will detect, but not
attach, a card.

The reason is that without this it comes up as a de card, which is
quite wrong.  It isn't a de card at all, it just smells somewhat like
one.  When the serial ROM can't be read a long line of gibberish
appears, and the de1 (in my case) interface remains.

I'd like to see this, I suppose:

lmc0:  found, but not attached in install kernels.

rather than:

de1:  can't read ENET ROM (why=3) (137600050000000000000000000000000000000000000000000000000000000000)

--Michael