dm: fdt: Add a function to decode phandles with arguments

For GPIOs and other functions we want to look up a phandle and then decode
a list of arguments for that phandle. Each phandle can have a different
number of arguments, specified by a property in the target node. This is
the "#gpio-cells" property for GPIOs.

Add a function to provide this feature, taken modified from Linux 3.18.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/fdtdec.h

@@ -178,6 +178,59 @@ enum fdt_compat_id {
 	COMPAT_COUNT,
 };
 
+#define MAX_PHANDLE_ARGS 16
+struct fdtdec_phandle_args {
+	int node;
+	int args_count;
+	uint32_t args[MAX_PHANDLE_ARGS];
+};
+
+/**
+ * fdtdec_parse_phandle_with_args() - Find a node pointed by phandle in a list
+ *
+ * This function is useful to parse lists of phandles and their arguments.
+ *
+ * Example:
+ *
+ * phandle1: node1 {
+ *	#list-cells = <2>;
+ * }
+ *
+ * phandle2: node2 {
+ *	#list-cells = <1>;
+ * }
+ *
+ * node3 {
+ *	list = <&phandle1 1 2 &phandle2 3>;
+ * }
+ *
+ * To get a device_node of the `node2' node you may call this:
+ * fdtdec_parse_phandle_with_args(blob, node3, "list", "#list-cells", 0, 1,
+ *				  &args);
+ *
+ * (This function is a modified version of __of_parse_phandle_with_args() from
+ * Linux 3.18)
+ *
+ * @blob:	Pointer to device tree
+ * @src_node:	Offset of device tree node containing a list
+ * @list_name:	property name that contains a list
+ * @cells_name:	property name that specifies the phandles' arguments count,
+ *		or NULL to use @cells_count
+ * @cells_count: Cell count to use if @cells_name is NULL
+ * @index:	index of a phandle to parse out
+ * @out_args:	optional pointer to output arguments structure (will be filled)
+ * @return 0 on success (with @out_args filled out if not NULL), -ENOENT if
+ *	@list_name does not exist, a phandle was not found, @cells_name
+ *	could not be found, the arguments were truncated or there were too
+ *	many arguments.
+ *
+ */
+int fdtdec_parse_phandle_with_args(const void *blob, int src_node,
+				   const char *list_name,
+				   const char *cells_name,
+				   int cell_count, int index,
+				   struct fdtdec_phandle_args *out_args);
+
 /* GPIOs are numbered from 0 */
 enum {
 	FDT_GPIO_NONE = -1U,	/* an invalid GPIO used to end our list */

lib/fdtdec.c

@@ -679,6 +679,130 @@ int fdtdec_get_bool(const void *blob, int node, const char *prop_name)
 	return cell != NULL;
 }
 
+int fdtdec_parse_phandle_with_args(const void *blob, int src_node,
+				   const char *list_name,
+				   const char *cells_name,
+				   int cell_count, int index,
+				   struct fdtdec_phandle_args *out_args)
+{
+	const __be32 *list, *list_end;
+	int rc = 0, size, cur_index = 0;
+	uint32_t count = 0;
+	int node = -1;
+	int phandle;
+
+	/* Retrieve the phandle list property */
+	list = fdt_getprop(blob, src_node, list_name, &size);
+	if (!list)
+		return -ENOENT;
+	list_end = list + size / sizeof(*list);
+
+	/* Loop over the phandles until all the requested entry is found */
+	while (list < list_end) {
+		rc = -EINVAL;
+		count = 0;
+
+		/*
+		 * If phandle is 0, then it is an empty entry with no
+		 * arguments.  Skip forward to the next entry.
+		 */
+		phandle = be32_to_cpup(list++);
+		if (phandle) {
+			/*
+			 * Find the provider node and parse the #*-cells
+			 * property to determine the argument length.
+			 *
+			 * This is not needed if the cell count is hard-coded
+			 * (i.e. cells_name not set, but cell_count is set),
+			 * except when we're going to return the found node
+			 * below.
+			 */
+			if (cells_name || cur_index == index) {
+				node = fdt_node_offset_by_phandle(blob,
+								  phandle);
+				if (!node) {
+					debug("%s: could not find phandle\n",
+					      fdt_get_name(blob, src_node,
+							   NULL));
+					goto err;
+				}
+			}
+
+			if (cells_name) {
+				count = fdtdec_get_int(blob, node, cells_name,
+						       -1);
+				if (count == -1) {
+					debug("%s: could not get %s for %s\n",
+					      fdt_get_name(blob, src_node,
+							   NULL),
+					      cells_name,
+					      fdt_get_name(blob, node,
+							   NULL));
+					goto err;
+				}
+			} else {
+				count = cell_count;
+			}
+
+			/*
+			 * Make sure that the arguments actually fit in the
+			 * remaining property data length
+			 */
+			if (list + count > list_end) {
+				debug("%s: arguments longer than property\n",
+				      fdt_get_name(blob, src_node, NULL));
+				goto err;
+			}
+		}
+
+		/*
+		 * All of the error cases above bail out of the loop, so at
+		 * this point, the parsing is successful. If the requested
+		 * index matches, then fill the out_args structure and return,
+		 * or return -ENOENT for an empty entry.
+		 */
+		rc = -ENOENT;
+		if (cur_index == index) {
+			if (!phandle)
+				goto err;
+
+			if (out_args) {
+				int i;
+
+				if (count > MAX_PHANDLE_ARGS) {
+					debug("%s: too many arguments %d\n",
+					      fdt_get_name(blob, src_node,
+							   NULL), count);
+					count = MAX_PHANDLE_ARGS;
+				}
+				out_args->node = node;
+				out_args->args_count = count;
+				for (i = 0; i < count; i++) {
+					out_args->args[i] =
+							be32_to_cpup(list++);
+				}
+			}
+
+			/* Found it! return success */
+			return 0;
+		}
+
+		node = -1;
+		list += count;
+		cur_index++;
+	}
+
+	/*
+	 * Result will be one of:
+	 * -ENOENT : index is for empty phandle
+	 * -EINVAL : parsing error on data
+	 * [1..n]  : Number of phandle (count mode; when index = -1)
+	 */
+	rc = index < 0 ? cur_index : -ENOENT;
+ err:
+	return rc;
+}
+
 /**
  * Decode a list of GPIOs from an FDT. This creates a list of GPIOs with no
  * terminating item.