vbnv: Do not silently reset cache in read_vbnv

Currently, read_vbnv performs a reset of the vbnv cache if it is not
valid. However, this information is not passed up to the vboot layer,
thus resulting in missed write-back of vbnv cache to storage if vboot
does not update the cache itself.

Update read_vbnv to return a value depending upon whether it wants a
write-back to be performed when save is called.
Return value:
0 = No write-back required
1 = Write-back of VBNV cache is required.

Change-Id: I239939d5f9731d89a9d53fe662321b93fc1ab113
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/15457
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/vendorcode/google/chromeos/vbnv.h b/src/vendorcode/google/chromeos/vbnv.h
index 5d21cc8481..a66d687fe5 100644
--- a/src/vendorcode/google/chromeos/vbnv.h
+++ b/src/vendorcode/google/chromeos/vbnv.h
@@ -19,7 +19,12 @@
 #include <types.h>
 
 /* Generic functions */
-void read_vbnv(uint8_t *vbnv_copy);
+/*
+ * Return value for read_vbnv:
+ * 1 = write-back of vbnv copy is required.
+ * 0 = otherwise
+ */
+int read_vbnv(uint8_t *vbnv_copy);
 void save_vbnv(const uint8_t *vbnv_copy);
 int verify_vbnv(uint8_t *vbnv_copy);
 int get_recovery_mode_from_vbnv(void);