On Thu, 2020-10-22 at 14:23 +0200, Ard Biesheuvel wrote:

quoted

+/**
+ * of_dma_get_max_cpu_address - Gets highest CPU address suitable for DMA
+ * @np: The node to start searching from or NULL to start from the root
+ *
+ * Gets the highest CPU physical address that is addressable by all DMA masters
+ * in the sub-tree pointed by np, or the whole tree if NULL is passed. If no
+ * DMA constrained device is found, it returns PHYS_ADDR_MAX.
+ */
+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;
+       struct of_range range;
+       const __be32 *ranges;
+       u64 cpu_end = 0;
+       int len;
+
+       if (!np)
+               np = of_root;
+
+       ranges = of_get_property(np, "dma-ranges", &len);
+       if (ranges && len) {
+               of_dma_range_parser_init(&parser, np);
+               for_each_of_range(&parser, &range)
+                       if (range.cpu_addr + range.size > cpu_end)
+                               cpu_end = range.cpu_addr + range.size;

Shouldn't this be 'range.cpu_addr + range.size - 1' ?

Yes, I agree. In that case arm64's counterpart should be:

	zone_dma_bits = max(32U, fls64(of_dma_get_max_cpu_address(NULL)));

I'll update it.

Regards,
Nicolas