+size_t dma_direct_max_mapping_size(struct device *dev)
+{
+	/*
+	 * Return the minimum of the direct DMA limit and the SWIOTLB limit.
+	 * Since direct DMA has no limit, it is fine to just return the SWIOTLB
+	 * limit.
+	 */
+	return swiotlb_max_mapping_size(dev);

Well, if we don't actually use the swiotlb buffers despite it being
compiled in or even allocated we don't need the limit.