fel: Support "-h" and "--help" options

Closes #96
Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>

fel.c

@@ -970,18 +970,10 @@ static void select_by_sid(const char *sid_arg, int *busnum, int *devnum)
 	free(list);
 }
 
-int main(int argc, char **argv)
-{
-	bool uboot_autostart = false; /* flag for "uboot" command = U-Boot autostart */
-	bool pflag_active = false; /* -p switch, causing "write" to output progress */
-	bool device_list = false; /* -l switch, prints device list and exits */
-	feldev_handle *handle;
-	int busnum = -1, devnum = -1;
-	char *sid_arg = NULL;
-
-	if (argc <= 1) {
+void usage(const char *cmd) {
 	puts("sunxi-fel " VERSION "\n");
 	printf("Usage: %s [options] command arguments... [command...]\n"
+		"	-h, --help			Print this usage summary and exit\n"
 		"	-v, --verbose			Verbose logging\n"
 		"	-p, --progress			\"write\" transfers show a progress bar\n"
 		"	-l, --list			Enumerate all (USB) FEL devices and exit\n"
@@ -1020,14 +1012,27 @@ int main(int argc, char **argv)
 		"	sid				Retrieve and output 128-bit SID key\n"
 		"	clear address length		Clear memory\n"
 		"	fill address length value	Fill memory\n"
-			, argv[0]
-		);
+		, cmd);
 	exit(0);
-	}
+}
+
+int main(int argc, char **argv)
+{
+	bool uboot_autostart = false; /* flag for "uboot" command = U-Boot autostart */
+	bool pflag_active = false; /* -p switch, causing "write" to output progress */
+	bool device_list = false; /* -l switch, prints device list and exits */
+	feldev_handle *handle;
+	int busnum = -1, devnum = -1;
+	char *sid_arg = NULL;
+
+	if (argc <= 1)
+		usage(argv[0]);
 
 	/* process all "prefix"-type arguments first */
 	while (argc > 1) {
-		if (strcmp(argv[1], "--verbose") == 0 || strcmp(argv[1], "-v") == 0)
+		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-h") == 0)
+			usage(argv[0]);
+		else if (strcmp(argv[1], "--verbose") == 0 || strcmp(argv[1], "-v") == 0)
 			verbose = true;
 		else if (strcmp(argv[1], "--progress") == 0 || strcmp(argv[1], "-p") == 0)
 			pflag_active = true;