Add ForceClear also on dev->normal transitions. Fix wrong API description.

vboot_firmware/lib/rollback_index.c

 /* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * Functions for querying, manipulating and locking rollback indices
  * stored in the TPM NVRAM.
  */
 
 #include "rollback_index.h"
 
@@ skipping 196 matching lines @@
 
 /* Checks for transitions between protected mode to developer mode.  When going
  * into developer mode, clear the TPM.
  */
 static uint32_t CheckDeveloperModeTransition(uint32_t current_developer) {
   uint32_t past_developer;
   int must_clear;
   RETURN_ON_FAILURE(TlclRead(DEVELOPER_MODE_NV_INDEX,
                              (uint8_t*) &past_developer,
                              sizeof(past_developer)));
-  must_clear = current_developer && !past_developer;
+  must_clear = current_developer != past_developer;
   if (must_clear) {
     RETURN_ON_FAILURE(TlclForceClear());
   }
   if (past_developer != current_developer) {
     /* (Unauthorized) writes to the TPM succeed even when the TPM is disabled
      * and deactivated.
      */
     RETURN_ON_FAILURE(TlclWrite(DEVELOPER_MODE_NV_INDEX,
                                 (uint8_t*) &current_developer,
                                 sizeof(current_developer)));
@@ skipping 127 matching lines @@
   return TPM_SUCCESS;
 }
 
 uint32_t LockFirmwareVersions() {
   return TlclSetGlobalLock();
 }
 
 uint32_t LockKernelVersionsByLockingPP() {
   return TlclLockPhysicalPresence();
 }