of: Support parsing phandle argument lists through a nexus node

Platforms like 96boards have a standardized connector/expansion
slot that exposes signals like GPIOs to expansion boards in an
SoC agnostic way. We'd like the DT overlays for the expansion
boards to be written once without knowledge of the SoC on the
other side of the connector. This avoids the unscalable
combinatorial explosion of a different DT overlay for each
expansion board and SoC pair.

We need a way to describe the GPIOs routed through the connector
in an SoC agnostic way. Let's introduce nexus property parsing
into the OF core to do this. This is largely based on the
interrupt nexus support we already have. This allows us to remap
a phandle list in a consumer node (e.g. reset-gpios) through a
connector in a generic way (e.g. via gpio-map). Do this in a
generic routine so that we can remap any sort of variable length
phandle list.

Taking GPIOs as an example, the connector would be a GPIO nexus,
supporting the remapping of a GPIO specifier space to multiple
GPIO providers on the SoC. DT would look as shown below, where
'soc_gpio1' and 'soc_gpio2' are inside the SoC, 'connector' is an
expansion port where boards can be plugged in, and
'expansion_device' is a device on the expansion board.

	soc {
		soc_gpio1: gpio-controller1 {
			#gpio-cells = <2>;
		};

		soc_gpio2: gpio-controller2 {
			#gpio-cells = <2>;
		};
	};

	connector: connector {
		#gpio-cells = <2>;
		gpio-map = <0 0 &soc_gpio1 1 0>,
			   <1 0 &soc_gpio2 4 0>,
			   <2 0 &soc_gpio1 3 0>,
			   <3 0 &soc_gpio2 2 0>;
		gpio-map-mask = <0xf 0x0>;
		gpio-map-pass-thru = <0x0 0x1>
	};

	expansion_device {
		reset-gpios = <&connector 2 GPIO_ACTIVE_LOW>;
	};

The GPIO core would use of_parse_phandle_with_args_map() instead
of of_parse_phandle_with_args() and arrive at the same type of
result, a phandle and argument list. The difference is that the
phandle and arguments will be remapped through the nexus node to
the underlying SoC GPIO controller node. In the example above,
we would remap 'reset-gpios' from <&connector 2 GPIO_ACTIVE_LOW>
to <&soc_gpio1 3 GPIO_ACTIVE_LOW>.

Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/base.c

@@ -1283,6 +1283,190 @@ int of_parse_phandle_with_args(const struct device_node *np, const char *list_na
 }
 EXPORT_SYMBOL(of_parse_phandle_with_args);
 
+/**
+ * of_parse_phandle_with_args_map() - Find a node pointed by phandle in a list and remap it
+ * @np:		pointer to a device tree node containing a list
+ * @list_name:	property name that contains a list
+ * @stem_name:	stem of property names that specify phandles' arguments count
+ * @index:	index of a phandle to parse out
+ * @out_args:	optional pointer to output arguments structure (will be filled)
+ *
+ * This function is useful to parse lists of phandles and their arguments.
+ * Returns 0 on success and fills out_args, on error returns appropriate errno
+ * value. The difference between this function and of_parse_phandle_with_args()
+ * is that this API remaps a phandle if the node the phandle points to has
+ * a <@stem_name>-map property.
+ *
+ * Caller is responsible to call of_node_put() on the returned out_args->np
+ * pointer.
+ *
+ * Example:
+ *
+ * phandle1: node1 {
+ *	#list-cells = <2>;
+ * }
+ *
+ * phandle2: node2 {
+ *	#list-cells = <1>;
+ * }
+ *
+ * phandle3: node3 {
+ * 	#list-cells = <1>;
+ * 	list-map = <0 &phandle2 3>,
+ * 		   <1 &phandle2 2>,
+ * 		   <2 &phandle1 5 1>;
+ *	list-map-mask = <0x3>;
+ * };
+ *
+ * node4 {
+ *	list = <&phandle1 1 2 &phandle3 0>;
+ * }
+ *
+ * To get a device_node of the `node2' node you may call this:
+ * of_parse_phandle_with_args(node4, "list", "list", 1, &args);
+ */
+int of_parse_phandle_with_args_map(const struct device_node *np,
+				   const char *list_name,
+				   const char *stem_name,
+				   int index, struct of_phandle_args *out_args)
+{
+	char *cells_name, *map_name = NULL, *mask_name = NULL;
+	char *pass_name = NULL;
+	struct device_node *cur, *new = NULL;
+	const __be32 *map, *mask, *pass;
+	static const __be32 dummy_mask[] = { [0 ... MAX_PHANDLE_ARGS] = ~0 };
+	static const __be32 dummy_pass[] = { [0 ... MAX_PHANDLE_ARGS] = 0 };
+	__be32 initial_match_array[MAX_PHANDLE_ARGS];
+	const __be32 *match_array = initial_match_array;
+	int i, ret, map_len, match;
+	u32 list_size, new_size;
+
+	if (index < 0)
+		return -EINVAL;
+
+	cells_name = kasprintf(GFP_KERNEL, "#%s-cells", stem_name);
+	if (!cells_name)
+		return -ENOMEM;
+
+	ret = -ENOMEM;
+	map_name = kasprintf(GFP_KERNEL, "%s-map", stem_name);
+	if (!map_name)
+		goto free;
+
+	mask_name = kasprintf(GFP_KERNEL, "%s-map-mask", stem_name);
+	if (!mask_name)
+		goto free;
+
+	pass_name = kasprintf(GFP_KERNEL, "%s-map-pass-thru", stem_name);
+	if (!pass_name)
+		goto free;
+
+	ret = __of_parse_phandle_with_args(np, list_name, cells_name, 0, index,
+					   out_args);
+	if (ret)
+		goto free;
+
+	/* Get the #<list>-cells property */
+	cur = out_args->np;
+	ret = of_property_read_u32(cur, cells_name, &list_size);
+	if (ret < 0)
+		goto put;
+
+	/* Precalculate the match array - this simplifies match loop */
+	for (i = 0; i < list_size; i++)
+		initial_match_array[i] = cpu_to_be32(out_args->args[i]);
+
+	ret = -EINVAL;
+	while (cur) {
+		/* Get the <list>-map property */
+		map = of_get_property(cur, map_name, &map_len);
+		if (!map) {
+			ret = 0;
+			goto free;
+		}
+		map_len /= sizeof(u32);
+
+		/* Get the <list>-map-mask property (optional) */
+		mask = of_get_property(cur, mask_name, NULL);
+		if (!mask)
+			mask = dummy_mask;
+		/* Iterate through <list>-map property */
+		match = 0;
+		while (map_len > (list_size + 1) && !match) {
+			/* Compare specifiers */
+			match = 1;
+			for (i = 0; i < list_size; i++, map_len--)
+				match &= !((match_array[i] ^ *map++) & mask[i]);
+
+			of_node_put(new);
+			new = of_find_node_by_phandle(be32_to_cpup(map));
+			map++;
+			map_len--;
+
+			/* Check if not found */
+			if (!new)
+				goto put;
+
+			if (!of_device_is_available(new))
+				match = 0;
+
+			ret = of_property_read_u32(new, cells_name, &new_size);
+			if (ret)
+				goto put;
+
+			/* Check for malformed properties */
+			if (WARN_ON(new_size > MAX_PHANDLE_ARGS))
+				goto put;
+			if (map_len < new_size)
+				goto put;
+
+			/* Move forward by new node's #<list>-cells amount */
+			map += new_size;
+			map_len -= new_size;
+		}
+		if (!match)
+			goto put;
+
+		/* Get the <list>-map-pass-thru property (optional) */
+		pass = of_get_property(cur, pass_name, NULL);
+		if (!pass)
+			pass = dummy_pass;
+
+		/*
+		 * Successfully parsed a <list>-map translation; copy new
+		 * specifier into the out_args structure, keeping the
+		 * bits specified in <list>-map-pass-thru.
+		 */
+		match_array = map - new_size;
+		for (i = 0; i < new_size; i++) {
+			__be32 val = *(map - new_size + i);
+
+			if (i < list_size) {
+				val &= ~pass[i];
+				val |= cpu_to_be32(out_args->args[i]) & pass[i];
+			}
+
+			out_args->args[i] = be32_to_cpu(val);
+		}
+		out_args->args_count = list_size = new_size;
+		/* Iterate again with new provider */
+		out_args->np = new;
+		of_node_put(cur);
+		cur = new;
+	}
+put:
+	of_node_put(cur);
+	of_node_put(new);
+free:
+	kfree(mask_name);
+	kfree(map_name);
+	kfree(cells_name);
+	kfree(pass_name);
+
+	return ret;
+}
+EXPORT_SYMBOL(of_parse_phandle_with_args_map);
+
 /**
  * of_parse_phandle_with_fixed_args() - Find a node pointed by phandle in a list
  * @np:		pointer to a device tree node containing a list

include/linux/of.h

@@ -363,6 +363,9 @@ extern struct device_node *of_parse_phandle(const struct device_node *np,
 extern int of_parse_phandle_with_args(const struct device_node *np,
 	const char *list_name, const char *cells_name, int index,
 	struct of_phandle_args *out_args);
+extern int of_parse_phandle_with_args_map(const struct device_node *np,
+	const char *list_name, const char *stem_name, int index,
+	struct of_phandle_args *out_args);
 extern int of_parse_phandle_with_fixed_args(const struct device_node *np,
 	const char *list_name, int cells_count, int index,
 	struct of_phandle_args *out_args);
@@ -815,6 +818,15 @@ static inline int of_parse_phandle_with_args(const struct device_node *np,
 	return -ENOSYS;
 }
 
+static inline int of_parse_phandle_with_args_map(const struct device_node *np,
+						 const char *list_name,
+						 const char *stem_name,
+						 int index,
+						 struct of_phandle_args *out_args)
+{
+	return -ENOSYS;
+}
+
 static inline int of_parse_phandle_with_fixed_args(const struct device_node *np,
 	const char *list_name, int cells_count, int index,
 	struct of_phandle_args *out_args)