lib/fmap: provide RW region device support

Explicitly provide a RW view of an FMAP region. This is required
for platforms which have separate implementations of a RO boot
device and a RW boot device.

BUG=chrome-os-partner:56151

Change-Id: Ibafa3dc534f53a3d90487f3190c0f8a2e82858c2
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/16203
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/include/fmap.h

@@ -27,6 +27,10 @@ int find_fmap_directory(struct region_device *fmrd);
  * 0 on success, < 0 on error. */
 int fmap_locate_area_as_rdev(const char *name, struct region_device *area);
 
+/* Just like fmap_locate_area_as_rdev(), however the region device is
+ * created from the RW boot device. */
+int fmap_locate_area_as_rdev_rw(const char *name, struct region_device *area);
+
 /* Locate the named area in the fmap and fill in a region with the
  * offset and size of that area within the boot media. Return 0 on success,
  * < 0 on error. */

src/lib/fmap.c

@@ -80,6 +80,16 @@ int fmap_locate_area_as_rdev(const char *name, struct region_device *area)
 	return boot_device_ro_subregion(&ar, area);
 }
 
+int fmap_locate_area_as_rdev_rw(const char *name, struct region_device *area)
+{
+	struct region ar;
+
+	if (fmap_locate_area(name, &ar))
+		return -1;
+
+	return boot_device_rw_subregion(&ar, area);
+}
+
 int fmap_locate_area(const char *name, struct region *ar)
 {
 	struct region_device fmrd;