From: Nishanth Aravamudan <redacted>
Date: Tue, 27 Oct 2015 15:20:10 -0700

Well, looks like I should spin up a v4 anyways for the powerpc changes.
So, to make sure I understand your point, should I make the generic
dma_get_page_shift a compile-error kind of thing? It will only fail on
architectures that actually build the NVME driver (as the only caller).
But I'm not sure how exactly to achieve that, if you could give a bit
more detail I'd appreciate it!

Yes, I am basically suggesting to simply not provide a default at all.