I've already talked with Christoph that we probably want to switch TTM
over to using that instead to also get rid of the ttm_io_prot() hack.
OK, would that mean us ditching other memory modes completely? And on-the-fly caching transitions? or is it just for the special case of cached coherent memory? Do we need to cache the coherent kernel mappings in TTM as well, for ttm_bo_kmap()?