On Thu, Oct 15, 2020 at 12:42 AM Christoph Hellwig [off-list ref] 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 prefer that of_root is not more widely exposed and NULL regularly
means 'the whole tree'.

Rob