purism/librem13v2: Add reading of serial number from CBFS

Check CBFS for 'serial_number' field, and use value if exists;
otherwise use value set at compile time.

Change-Id: I4b50f6310ca32b9dd372db075a5b5729e3b06619
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Signed-off-by: Youness Alaoui <youness.alaoui@puri.sm>
Reviewed-on: https://review.coreboot.org/22040
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/purism/librem13v2/mainboard.c

@@ -0,0 +1,49 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2017 Purism SPC
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <smbios.h>
+#include <string.h>
+#include <cbfs.h>
+
+#define MAX_SERIAL_LENGTH 0x100
+
+const char *smbios_mainboard_serial_number(void)
+{
+	static char serial_number[MAX_SERIAL_LENGTH + 1] = {0};
+	struct cbfsf file;
+
+	if (serial_number[0] != 0)
+		return serial_number;
+
+	if (cbfs_boot_locate(&file, "serial_number", NULL) == 0) {
+		struct region_device cbfs_region;
+		size_t serial_len;
+
+		cbfs_file_data(&cbfs_region, &file);
+
+		serial_len = region_device_sz(&cbfs_region);
+		if (serial_len <= MAX_SERIAL_LENGTH) {
+			if (rdev_readat(&cbfs_region, serial_number, 0,
+					serial_len) == serial_len) {
+				serial_number[serial_len] = 0;
+				return serial_number;
+			}
+		}
+	}
+
+	strncpy(serial_number, CONFIG_MAINBOARD_SERIAL_NUMBER, MAX_SERIAL_LENGTH);
+
+	return serial_number;
+}