quoted

to preserve the legacy behavior rather than changing the behavior of
every usbnet driver all at once?  Like make a new
usbnet_get_link_ksettings_nonmdio and update only cdc_ncm to use it?

Then I would have to touch them all. The problem is that the MDIO
stuff really is pretty much a layering violation. It should never
have been default. But now it is.

I don't understand this.  Your 0001 patch changes the behavior of
usbnet_get_link_ksettings() and you have to touch all of the 8 drivers
that use it if you don't want to change their behavior.  If you keep
the old usbnet_get_link_ksettings() and add
usbnet_get_link_ksettings_nonmdio() then you can just update cdc_ncm
to start with, and then gradually migrate other drivers.  And
eventually fix the layering violation and get rid of the legacy
function when the whole transition is done.

 - R.