Re: [PATCH v3 4/5] cmd: fdt: add 'fdt fit' to prepare a devicetree for other boot commands

[David Lechner <dlechner@baylibre.com>]

On 10/26/26 7:18 AM, Carlo Caione wrote:
> A board may keep its devicetree and overlays in a FIT while booting
> a kernel or EFI application from elsewhere. Boot scripts need a way
> to verify and assemble that devicetree without asking bootm to boot
> the FIT.
> 

...

> +/*
> + * fdt fit <addr>[#<conf>] <dest> [<length>]
> + *
> + * Load the devicetree of a FIT configuration, with its overlays applied, and
> + * copy it to <dest>. Images are always verified, so the configuration must
> + * also satisfy any required signature in the control devicetree. Unlike bootm,
> + * image load addresses are ignored and configurations cannot be chained.
> + */
> +static int fdt_fit(int argc, char *const argv[])
> +{
> +	struct bootm_headers images = { .verify = 1 };
> +	const char *conf = NULL;
> +	ulong addr, dest, data, len;
> +	bool owned;
> +	void *fdt;
> +	int ret;
> +
> +	if (argc < 2 || argc > 3)
> +		return CMD_RET_USAGE;
> +
> +	if (!fit_parse_conf(argv[0], image_load_addr, &addr, &conf))
> +		addr = hextoul(argv[0], NULL);
> +	dest = hextoul(argv[1], NULL);
> +
> +	/* Only a single configuration authenticates the whole combination */
> +	if (conf && strchr(conf, '#')) {
> +		puts("Chained configurations are not supported\n");
> +		return CMD_RET_FAILURE;
> +	}
> +
> +	if (boot_get_fdt_fit(&images, addr, NULL, &conf, IH_ARCH_DEFAULT,
> +			     FIT_LOAD_PREPARE, &data, &len, &owned) < 0)
> +		return CMD_RET_FAILURE;
> +
> +	fdt = map_sysmem(data, len);
> +	ret = CMD_RET_FAILURE;
> +	if (fdt_check_full(fdt, len)) {
> +		puts("Invalid FDT in FIT\n");
> +		goto out;
> +	}
> +
> +	len = fdt_totalsize(fdt);
> +	if (argc > 2) {
> +		ulong newlen = hextoul(argv[2], NULL);
> +
> +		if (newlen < len) {
> +			printf("New length 0x%lX < existing length 0x%lX, aborting.\n",
> +			       newlen, len);
> +			goto out;
> +		}
> +		len = newlen;
> +	}
> +
> +	if (CONFIG_IS_ENABLED(LMB) && lmb_read_check(dest, len)) {
> +		puts("ERROR: trying to overwrite reserved memory...\n");
> +		goto out;
> +	}
> +
> +	ret = fdt_open_into(fdt, map_sysmem(dest, len), len);

nit: its a bit awkward to use ret for both CMD_RET_ and other error type.
Would suggest to replace this one with e.g. err.

> +	if (ret) {
> +		printf("libfdt fdt_open_into(): %s\n", fdt_strerror(ret));
> +		ret = CMD_RET_FAILURE;

Then we don't have to rember to restore the value that was already in ret
here.

> +		goto out;
> +	}
> +	ret = CMD_RET_SUCCESS;
> +
> +out:
> +	if (owned)
> +		free(fdt);
> +
> +	return ret;
> +}
> +