+	/*
+	 * fallback to default mapping if driver doesn't provide
+	 * get_queue_affinity callback
+	 */
+	if (!get_queue_affinity) {
+		fallback = true;
+		goto fallback;
+	}
+
+	for (queue = 0; queue < qmap->nr_queues; queue++) {
+		mask = get_queue_affinity(dev_data, dev_off, queue);
+		if (!mask)
+			goto fallback;
+
+		for_each_cpu(cpu, mask)
+			qmap->mq_map[cpu] = qmap->queue_offset + queue;
+	}
+
+	return 0;
+
+fallback:
+	if (!fallback) {
+		WARN_ON_ONCE(qmap->nr_queues > 1);
+		blk_mq_clear_mq_map(qmap);
+		return 0;
+	}
+	return blk_mq_map_queues(qmap);

Please remove the NULL get_affinity case and let the callers handle
the fallback.  Also I think it makes sense to leave the !mask fallback
case to the callers as well to simplify the calling conventions.