coreboot: introduce boot_device

The boot_device is a region_device that represents the
device from which coreboot retrieves and boots its stages.
The existing cbfs implementations use the boot_device as
the intermediary for accessing the CBFS region. Also,
there's currently only support for a read-only view of
the boot_device. i.e. one cannot write to the boot_device
using this view. However, a writable boot_device could
be added in the future.

Change-Id: Ic0da796ab161b8025c90631be3423ba6473ad31c
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10216
Tested-by: build bot (Jenkins)
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/lib/boot_device.c

@@ -0,0 +1,38 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2015 Google Inc.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc.
+ */
+
+#include <boot_device.h>
+
+void __attribute__((weak)) boot_device_init(void)
+{
+	/* Provide weak do-nothing init. */
+}
+
+int boot_device_ro_subregion(const struct region *sub,
+				struct region_device *subrd)
+{
+	const struct region_device *boot_dev;
+
+	boot_dev = boot_device_ro();
+
+	if (boot_dev == NULL)
+		return -1;
+
+	return rdev_chain(subrd, boot_dev, region_offset(sub), region_sz(sub));
+}