Pay attention to TPM communication errors

firmware/lib/tpm_lite/include/tlcl.h

 /* 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.
  */
 
 /* TPM Lightweight Command Library.
  *
  * A low-level library for interfacing to TPM hardware or an emulator.
  */
 
 #ifndef TPM_LITE_TLCL_H_
 #define TPM_LITE_TLCL_H_
 
 #include "sysincludes.h"
 
 /*****************************************************************************/
 /* Functions to be implemented by the stub library */
 
 /* Initialize the stub library */
 void TlclStubInit(void);
 
 /* Close and open the device.  This is needed for running more complex commands
  * at user level, such as TPM_TakeOwnership, since the TPM device can be opened
  * only by one process at a time.
  */
 void TlclCloseDevice(void);
 void TlclOpenDevice(void);
 
-void TlclStubSendReceive(uint8_t* request, int request_length,
-                         uint8_t* response, int max_length);
+/* Send data to the TPM and receive a response.  Returns 0 if success,
+ * nonzero if error. */
+uint32_t TlclStubSendReceive(uint8_t* request, int request_length,
+                             uint8_t* response, int max_length);
 
 /*****************************************************************************/
 /* Functions implemented in tlcl.c */
 
 /* Call this first.
  */
 void TlclLibInit(void);
 
-
 /* Logs to stdout.  Arguments like printf.
  */
 void TlclLog(char* format, ...);
 
 /* Sets the log level.  0 is quietest.
  */
 void TlclSetLogLevel(int level);
 
 /* Sends a TPM_Startup(ST_CLEAR).  The TPM error code is returned (0
  * for success).
@@ skipping 59 matching lines @@
 
 /* Issues a PhysicalDisable.  The TPM error code is returned.
  */
 uint32_t TlclClearEnable(void);
 
 /* Issues a SetDeactivated.  Pass 0 to activate.  Returns result code.
  */
 uint32_t TlclSetDeactivated(uint8_t flag);
 
 /* Gets flags of interest.  Pointers for flags you aren't interested in may
- * be NULL.  The TPM error code is returned.  
+ * be NULL.  The TPM error code is returned.
  */
 uint32_t TlclGetFlags(uint8_t* disable, uint8_t* deactivated, uint8_t* nvlocked);
 
 /* Sets the bGlobalLock flag, which only a reboot can clear.  The TPM error
  * code is returned.
  */
 uint32_t TlclSetGlobalLock(void);
 
 /* Performs a TPM_Extend.
  */
 uint32_t TlclExtend(int pcr_num, uint8_t* in_digest, uint8_t* out_digest);
 
 /* Gets the permission bits for the NVRAM space with |index|.
  */
 uint32_t TlclGetPermissions(uint32_t index, uint32_t* permissions);
 
 #endif  /* TPM_LITE_TLCL_H_ */