On Thu, 2020-10-15 at 07:42 +0200, Christoph Hellwig wrote:

quoted

+phys_addr_t __init of_dma_get_max_cpu_address(struct device_node *np)
+{
+	phys_addr_t max_cpu_addr = PHYS_ADDR_MAX;
+	struct of_range_parser parser;
+	phys_addr_t subtree_max_addr;
+	struct device_node *child;
+	phys_addr_t cpu_end = 0;
+	struct of_range range;
+	const __be32 *ranges;
+	int len;
+
+	if (!np)
+		np = of_root;

Requiring of_root to be passed explicitly would seem more natural
to me than the magic NULL argument.  There doesn't seem to be any
precedent for that kind of calling convention either.

I inspired that behavior from __of_find_all_nodes(). I'll change it.