mmio_rb_lookup
if (mmio_rb_lookup(&mmio_rb_root, paddr, &entry) == 0) {
} else if (mmio_rb_lookup(&mmio_rb_fallback, paddr, &entry)) {
if (mmio_rb_lookup(rbt, memp->base, &entry) != 0)
err = mmio_rb_lookup(&mmio_rb_root, memp->base, &entry);