of: address: Add support for the parent DMA bus

Some SoCs have devices that are using a separate bus from the main bus to
perform DMA.

These buses might have some restrictions and/or different mapping than from
the CPU side, so we'd need to express those using the usual dma-ranges, but
using a different DT node than the node's parent.

Now that the generic interconnect bindings are available, we can model an
interconnect with the reserved name "dma-mem" for those use-cases.

Reviewed-by: Robin Murphy <[e-mail]>
Signed-off-by: Maxime Ripard <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

drivers/of/address.c

···
 }
 EXPORT_SYMBOL(of_translate_address);
 
+static struct device_node *__of_get_dma_parent(const struct device_node *np)
+{
+	struct of_phandle_args args;
+	int ret, index;
+
+	index = of_property_match_string(np, "interconnect-names", "dma-mem");
+	if (index < 0)
+		return of_get_parent(np);
+
+	ret = of_parse_phandle_with_args(np, "interconnects",
+					 "#interconnect-cells",
+					 index, &args);
+	if (ret < 0)
+		return of_get_parent(np);
+
+	return of_node_get(args.np);
+}
+
 u64 of_translate_dma_address(struct device_node *dev, const __be32 *in_addr)
 {
 	struct device_node *host;
 	u64 ret;
 
-	ret = __of_translate_address(dev, of_get_parent,
+	ret = __of_translate_address(dev, __of_get_dma_parent,
 				     in_addr, "dma-ranges", &host);
 
 	if (host) {
···
 		return -EINVAL;
 
 	while (1) {
+		struct device_node *parent;
+
 		naddr = of_n_addr_cells(node);
 		nsize = of_n_size_cells(node);
-		node = of_get_next_parent(node);
+
+		parent = __of_get_dma_parent(node);
+		of_node_put(node);
+
+		node = parent;
 		if (!node)
 			break;