Re: [PATCH v2 3/6] Add fdtget utility to read property values from device tree

On Wed, Sep 07, 2011 at 12:54:17PM -0700, Simon Glass wrote:

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>][<format>]	Type of data
	-h		Print this help

	<type>		One character (s=string, i=int, u=unsigned, b=byte)
	<format>	Optional format character (x=hex)

It is not terribly clear how these are combined.

Is there any way to make these more closely resemble printf() style
format specifiers?

"and perhaps property"?  AFAICT this will SEGV if property is NULL.

+ * @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) {
+		show_data(disp, value, len);
+		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 = util_read_fdt(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>][<format>]\tType of data\n"
+	"\t-h\t\tPrint this help\n\n"
+	"\t<type>\t\tOne character (s=string, i=int, u=unsigned, b=byte)\n"
+	"\t<format>\tOptional format character (x=hex)\n";
+
+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;
+
+	memset(&disp, '\0', sizeof(disp));
+	for (;;) {
+		int c = getopt(argc, argv, "ht:");
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'h':
+		case '?':
+			usage("");
+
+		case 't':
+			if (utilfdt_decode_type(optarg, &disp.type,
+					&disp.format))
+				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;
+}

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson