lib/cbfs: Add fallback to RO region to cbfs_boot_locate

With this change cbfs_boot_locate will check the RO (COREBOOT) region if
a file can not be found in the active RW region. By doing so it is not
required to duplicate static files that are not intended to be updated
to the RW regions.

The coreboot image can still be updated by adding the file to the RW
region.

This change is intended to support VBOOT on systems with a small flash
device.

BUG=N/A
TEST=tested on facebook fbg1701

Change-Id: I81ceaf927280cef9a3f09621c796c451e9115211
Signed-off-by: Wim Vervoorn <wvervoorn@eltan.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36545
Reviewed-by: Frans Hendriks <fhendriks@eltan.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/lib/cbfs.c b/src/lib/cbfs.c
index 9ac1bc084b..13b5afb6ea 100644
--- a/src/lib/cbfs.c
+++ b/src/lib/cbfs.c
@@ -62,6 +62,22 @@ int cbfs_boot_locate(struct cbfsf *fh, const char *name, uint32_t *type)
 	}
 
 	int ret = cbfs_locate(fh, &rdev, name, type);
+
+	if (CONFIG(VBOOT_ENABLE_CBFS_FALLBACK) && ret) {
+
+		/*
+		 * When VBOOT_ENABLE_CBFS_FALLBACK is enabled and a file is not available in the
+		 * active RW region, the RO (COREBOOT) region will be used to locate the file.
+		 *
+		 * This functionality makes it possible to avoid duplicate files in the RO
+		 * and RW partitions while maintaining updateability.
+		 *
+		 * Files can be added to the RO_REGION_ONLY config option to use this feature.
+		 */
+		printk(BIOS_DEBUG, "Fall back to RO region for %s\n", name);
+		ret = cbfs_locate_file_in_region(fh, "COREBOOT", name, type);
+	}
+
 	if (!ret)
 		if (vboot_measure_cbfs_hook(fh, name))
 			return -1;