lib/efi_loader/efi_fdt.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Bootmethod for distro boot via EFI
 *
 * Copyright 2021 Google LLC
 * Written by Simon Glass <sjg@chromium.org>
 */

#include <efi_loader.h>
#include <env.h>
#include <errno.h>
#include <log.h>
#include <string.h>
#include <vsprintf.h>

/**
 * distro_efi_get_fdt_name() - get the filename for reading the .dtb file
 *
 * @fname:	buffer for filename
 * @size:	buffer size
 * @seq:	sequence number, to cycle through options (0=first)
 *
 * Returns:
 * 0 on success,
 * -ENOENT if the "fdtfile" env var does not exist,
 * -EINVAL if there are no more options,
 * -EALREADY if the control FDT should be used
 */
int efi_get_distro_fdt_name(char *fname, int size, int seq)
{
	const char *fdt_fname;
	const char *prefix;

	/* select the prefix */
	switch (seq) {
	case 0:
		/* this is the default */
		prefix = "/dtb";
		break;
	case 1:
		prefix = "";
		break;
	case 2:
		prefix = "/dtb/current";
		break;
	default:
		return log_msg_ret("pref", -EINVAL);
	}

	fdt_fname = env_get("fdtfile");
	if (fdt_fname) {
		snprintf(fname, size, "%s/%s", prefix, fdt_fname);
		log_debug("Using device tree: %s\n", fname);
	} else if (IS_ENABLED(CONFIG_OF_HAS_PRIOR_STAGE)) {
		strcpy(fname, "<prior>");
		return log_msg_ret("pref", -EALREADY);
	/* Use this fallback only for 32-bit ARM */
	} else if (IS_ENABLED(CONFIG_ARM) && !IS_ENABLED(CONFIG_ARM64)) {
		const char *soc = env_get("soc");
		const char *board = env_get("board");
		const char *boardver = env_get("boardver");

		/* cf the code in label_boot() which seems very complex */
		snprintf(fname, size, "%s/%s%s%s%s.dtb", prefix,
			 soc ? soc : "", soc ? "-" : "", board ? board : "",
			 boardver ? boardver : "");
		log_debug("Using default device tree: %s\n", fname);
	} else {
		return log_msg_ret("env", -ENOENT);
	}

	return 0;
}