Add fdtget utility to read property values from a device tree

This simply utility makes it easy for scripts to read values from the device
tree. It is written in C and uses the same libfdt as the rest of the dtc
package.

What is it for:
- Reading fdt values from scripts
- Extracting fdt information within build systems
- Looking at particular values without having to dump the entire tree

To use it, specify the fdt binary file on command line followed by a list of
node, property pairs. The utility then looks up each node, finds the property
and displays the value.

Each value is printed on a new line.

fdtget tries to guess the type of each property based on its contents. This
is not always reliable, so you can use the -t option to force fdtget to decode
the value as a string, or byte, etc.

To read from stdin, use - as the file.

Usage:
	fdtget <options> <dt file> [<node> <property>]...
Options:
	-t <type>	Type of data
	-h		Print this help

<type>	s=string, i=int, u=unsigned, x=hex
	Optional modifier prefix:
		hh or b=byte, h=2 byte, l=4 byte (default)

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

fdtget.c

@@ -0,0 +1,226 @@
+/*
+ * Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+#include <ctype.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <libfdt.h>
+
+#include "util.h"
+
+/* Holds information which controls our output and options */
+struct display_info {
+	int type;		/* data type (s/i/u/x or 0 for default) */
+	int size;		/* data size (1/2/4) */
+};
+
+static void report_error(const char *where, int err)
+{
+	fprintf(stderr, "Error at '%s': %s\n", where, fdt_strerror(err));
+}
+
+/**
+ * Displays data of a given length according to selected options
+ *
+ * If a specific data type is provided in disp, then this is used. Otherwise
+ * we try to guess the data type / size from the contents.
+ *
+ * @param disp		Display information / options
+ * @param data		Data to display
+ * @param len		Maximum length of buffer
+ * @return 0 if ok, -1 if data does not match format
+ */
+static int show_data(struct display_info *disp, const char *data, int len)
+{
+	int i, size;
+	const uint8_t *p = (const uint8_t *)data;
+	const char *s;
+	int value;
+	int is_string;
+	char fmt[3];
+
+	/* no data, don't print */
+	if (len == 0)
+		return 0;
+
+	is_string = (disp->type) == 's' ||
+		(!disp->type && util_is_printable_string(data, len));
+	if (is_string) {
+		if (data[len - 1] != '\0') {
+			fprintf(stderr, "Unterminated string\n");
+			return -1;
+		}
+		for (s = data; s - data < len; s += strlen(s) + 1) {
+			if (s != data)
+				printf(" ");
+			printf("%s", (const char *)s);
+		}
+		return 0;
+	}
+	size = disp->size;
+	if (size == -1)
+		size = (len % 4) == 0 ? 4 : 1;
+	else if (len % size) {
+		fprintf(stderr, "Property length must be a multiple of "
+				"selected data size\n");
+		return -1;
+	}
+	fmt[0] = '%';
+	fmt[1] = disp->type ? disp->type : 'd';
+	fmt[2] = '\0';
+	for (i = 0; i < len; i += size, p += size) {
+		if (i)
+			printf(" ");
+		value = size == 4 ? fdt32_to_cpu(*(const uint32_t *)p) :
+			size == 2 ? (*p << 8) | p[1] : *p;
+		printf(fmt, value);
+	}
+	return 0;
+}
+
+/**
+ * Show the data for a given node (and perhaps property) according to the
+ * display option provided.
+ *
+ * @param blob		FDT blob
+ * @param disp		Display information / options
+ * @param node		Node to display
+ * @param property	Name of property to display, or NULL if none
+ * @return 0 if ok, -ve on error
+ */
+static int show_data_for_item(const void *blob, struct display_info *disp,
+		int node, const char *property)
+{
+	const void *value = NULL;
+	int len, err = 0;
+
+	value = fdt_getprop(blob, node, property, &len);
+	if (value) {
+		if (show_data(disp, value, len))
+			err = -1;
+		else
+			printf("\n");
+	} else {
+		report_error(property, len);
+		err = -1;
+	}
+	return err;
+}
+
+/**
+ * Run the main fdtget operation, given a filename and valid arguments
+ *
+ * @param disp		Display information / options
+ * @param filename	Filename of blob file
+ * @param arg		List of arguments to process
+ * @param arg_count	Number of arguments
+ * @param return 0 if ok, -ve on error
+ */
+static int do_fdtget(struct display_info *disp, const char *filename,
+		     char **arg, int arg_count)
+{
+	char *blob;
+	int i, node;
+
+	blob = utilfdt_read(filename);
+	if (!blob)
+		return -1;
+
+	for (i = 0; i + 2 <= arg_count; i += 2) {
+		node = fdt_path_offset(blob, arg[0]);
+		if (node < 0) {
+			report_error(arg[0], node);
+			return -1;
+		}
+
+		if (show_data_for_item(blob, disp, node, arg[1]))
+			return -1;
+	}
+	return 0;
+}
+
+static const char *usage_msg =
+	"fdtget - read values from device tree\n"
+	"\n"
+	"Each value is printed on a new line.\n\n"
+	"Usage:\n"
+	"	fdtget <options> <dt file> [<node> <property>]...\n"
+	"Options:\n"
+	"\t-t <type>\tType of data\n"
+	"\t-h\t\tPrint this help\n\n"
+	USAGE_TYPE_MSG;
+
+static void usage(const char *msg)
+{
+	if (msg)
+		fprintf(stderr, "Error: %s\n\n", msg);
+
+	fprintf(stderr, "%s", usage_msg);
+	exit(2);
+}
+
+int main(int argc, char *argv[])
+{
+	char *filename = NULL;
+	struct display_info disp;
+
+	/* set defaults */
+	memset(&disp, '\0', sizeof(disp));
+	disp.size = -1;
+	for (;;) {
+		int c = getopt(argc, argv, "ht:");
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'h':
+		case '?':
+			usage(NULL);
+
+		case 't':
+			if (utilfdt_decode_type(optarg, &disp.type,
+					&disp.size))
+				usage("Invalid type string");
+			break;
+		}
+	}
+
+	if (optind < argc)
+		filename = argv[optind++];
+	if (!filename)
+		usage("Missing filename");
+
+	argv += optind;
+	argc -= optind;
+
+	/* Allow no arguments, and silently succeed */
+	if (!argc)
+		return 0;
+
+	/* Check for node, property arguments */
+	if (argc % 2)
+		usage("Must have an even number of arguments");
+
+	if (do_fdtget(&disp, filename, argv, argc))
+		return 1;
+	return 0;
+}