[RFC PATCH 71/77] Add fdtaddon tool to apply an addon

libfdt has support for applying an addon on top of a base device-tree.
This is provided by the libfdt fdt_addon_apply() function.

The fdtaddon tool is command line tool which allows to apply addon dtb
file to a base device-tree dtb file. It relies on fdt_addon_apply().

Signed-off-by: Herve Codina <[email protected]>
---
 Makefile    |   5 ++
 fdtaddon.c  | 197 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 meson.build |   2 +-
 3 files changed, 203 insertions(+), 1 deletion(-)
 create mode 100644 fdtaddon.c

diff --git a/Makefile b/Makefile
index 83d8220..1137cee 100644
--- a/Makefile
+++ b/Makefile
@@ -159,6 +159,7 @@ BIN += fdtdump
 BIN += fdtget
 BIN += fdtput
 BIN += fdtoverlay
+BIN += fdtaddon
 
 SCRIPTS = dtdiff
 
@@ -172,6 +173,7 @@ ifneq ($(MAKECMDGOALS),libfdt)
 -include $(FDTGET_OBJS:%.o=%.d)
 -include $(FDTPUT_OBJS:%.o=%.d)
 -include $(FDTOVERLAY_OBJS:%.o=%.d)
+-include $(FDTADDON_OBJS:%.o=%.d)
 endif
 endif
 
@@ -255,6 +257,8 @@ fdtput:	$(FDTPUT_OBJS) $(LIBFDT_dep)
 
 fdtoverlay: $(FDTOVERLAY_OBJS) $(LIBFDT_dep)
 
+fdtaddon: $(FDTADDON_OBJS) $(LIBFDT_dep)
+
 dist:
 	git archive --format=tar --prefix=dtc-$(dtc_version)/ HEAD \
 		> ../dtc-$(dtc_version).tar
@@ -295,6 +299,7 @@ TESTS_BIN += fdtput
 TESTS_BIN += fdtget
 TESTS_BIN += fdtdump
 TESTS_BIN += fdtoverlay
+TESTS_BIN += fdtaddon
 
 ifneq ($(MAKECMDGOALS),libfdt)
 include tests/Makefile.tests
diff --git a/fdtaddon.c b/fdtaddon.c
new file mode 100644
index 0000000..c2fefa3
--- /dev/null
+++ b/fdtaddon.c
@@ -0,0 +1,197 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2025 Bootlin. All rights reserved.
+ *
+ * Author:
+ *	 Herve Codina <[email protected]>
+ */
+
+#include <assert.h>
+#include <ctype.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <inttypes.h>
+
+#include <libfdt.h>
+
+#include "util.h"
+
+/* Usage related data. */
+static const char usage_synopsis[] =
+	"apply an addon to a base blob\n"
+	"	fdtaddon <options> <addon.dtba>";
+static const char usage_short_opts[] = "i:o:t:v" USAGE_COMMON_SHORT_OPTS;
+static const struct option usage_long_opts[] = {
+	{ "input", required_argument, NULL, 'i' },
+	{ "output", required_argument, NULL, 'o' },
+	{ "target", required_argument, NULL, 't' },
+	{ "verbose", no_argument, NULL, 'v' },
+	USAGE_COMMON_LONG_OPTS,
+};
+static const char *const usage_opts_help[] = { "Input base DT blob",
+					       "Output DT blob", "Target node",
+					       "Verbose messages",
+					       USAGE_COMMON_OPTS_HELP };
+
+int verbose;
+
+static void *do_apply(void *base, const void *addon, const char *target)
+{
+	void *tmp_merged;
+	void *tmp_addon;
+	size_t max_merged_size;
+	int ret;
+
+	/*
+	 * We take copies first, because a failed apply can trash
+	 * both the base blob and the overlay.
+	 */
+
+	/*
+	 * The merged size should not be greater than the sum of the size of
+	 * individual items.
+	 */
+	max_merged_size = fdt_totalsize(base) + fdt_totalsize(addon);
+
+	tmp_merged = xmalloc(max_merged_size);
+	ret = fdt_open_into(base, tmp_merged, max_merged_size);
+	if (ret) {
+		fprintf(stderr,
+			"\nFailed to make temporary copy: %s\n",
+			fdt_strerror(ret));
+		goto fail;
+	}
+
+	tmp_addon = xmalloc(fdt_totalsize(addon));
+	memcpy(tmp_addon, addon, fdt_totalsize(addon));
+
+	if (!(fdt_dt_flags(tmp_addon) & FDT_FLAG_ADDON)) {
+		fprintf(stderr,
+			"\nAddon dtb is not an 'addon'\n");
+		goto fail;
+	}
+
+	ret = fdt_addon_apply(tmp_merged, tmp_addon, target);
+	if (ret) {
+		fprintf(stderr, "\nFailed to apply %s\n", fdt_strerror(ret));
+		goto fail;
+	}
+
+	free(tmp_addon);
+	return tmp_merged;
+
+fail:
+	free(tmp_merged);
+	free(tmp_addon);
+	return NULL;
+}
+
+static int do_fdtaddon(const char *input_filename, const char *output_filename,
+		       const char *addon_filename, const char *target)
+{
+	void *base_blob = NULL;
+	void *addon_blob = NULL;
+	void *merged_blob = NULL;
+	size_t base_buflen;
+	size_t addon_buflen;
+	int ret = -1;
+
+	base_blob = utilfdt_read(input_filename, &base_buflen);
+	if (!base_blob) {
+		fprintf(stderr, "\nFailed to read '%s'\n", input_filename);
+		goto out_err;
+	}
+	if (fdt_totalsize(base_blob) > base_buflen) {
+		fprintf(stderr,
+			"\nBase blob is incomplete (%zu / %"PRIu32" bytes read)\n",
+			base_buflen, fdt_totalsize(base_blob));
+		goto out_err;
+	}
+
+	addon_blob = utilfdt_read(addon_filename, &addon_buflen);
+	if (!addon_blob) {
+		fprintf(stderr, "\nFailed to read '%s'\n", addon_filename);
+		goto out_err;
+	}
+	if (fdt_totalsize(addon_blob) > addon_buflen) {
+		fprintf(stderr,
+			"\nAddon blob is incomplete (%zu / %"PRIu32" bytes read)\n",
+			addon_buflen, fdt_totalsize(addon_blob));
+		goto out_err;
+	}
+
+	/* apply the addon  */
+	merged_blob = do_apply(base_blob, addon_blob, target);
+	if (!merged_blob)
+		goto out_err;
+
+	fdt_pack(merged_blob);
+	ret = utilfdt_write(output_filename, merged_blob);
+	if (ret)
+		fprintf(stderr, "\nFailed to write '%s'\n", output_filename);
+
+out_err:
+	free(merged_blob);
+	free(addon_blob);
+	free(base_blob);
+
+	return ret;
+}
+
+int main(int argc, char *argv[])
+{
+	char *input_filename = NULL;
+	char *output_filename = NULL;
+	char *addon_filename = NULL;
+	const char *target = NULL;
+	int opt;
+
+	while ((opt = util_getopt_long()) != EOF) {
+		switch (opt) {
+		case_USAGE_COMMON_FLAGS
+
+		case 'i':
+			input_filename = optarg;
+			break;
+		case 'o':
+			output_filename = optarg;
+			break;
+		case 'v':
+			verbose = 1;
+			break;
+		case 't':
+			target = optarg;
+			break;
+		}
+	}
+
+	if (!input_filename)
+		usage("missing input file");
+
+	if (!output_filename)
+		usage("missing output file");
+
+	if (!target)
+		usage("missing target");
+
+	argv += optind;
+	argc -= optind;
+
+	if (argc != 1)
+		usage("missing addon file");
+
+	addon_filename = argv[0];
+
+	if (verbose) {
+		printf("input  = %s\n", input_filename);
+		printf("output = %s\n", output_filename);
+		printf("addon = %s\n", addon_filename);
+	}
+
+	if (do_fdtaddon(input_filename, output_filename, addon_filename, target))
+		return 1;
+
+	return 0;
+}
diff --git a/meson.build b/meson.build
index 66b44e8..c108514 100644
--- a/meson.build
+++ b/meson.build
@@ -107,7 +107,7 @@ if get_option('tools') and not wheel_only
     install: true,
   )
 
-  foreach e: ['fdtdump', 'fdtget', 'fdtput', 'fdtoverlay']
+  foreach e: ['fdtdump', 'fdtget', 'fdtput', 'fdtoverlay', 'fdtaddon']
     dtc_tools += executable(e, files(e + '.c'), dependencies: util_dep, install: true)
   endforeach
 
-- 
2.52.0