Clear TPM if software firmware WP is disabled

Change-Id: I98d111d70e777b616cb2d09ec7e2b5d982f3a91e

R=bleung@chromium.org
BUG=chrome-os-partner:3317
TEST=manual

Install R12 release with kernel version 0x00020001.
Run `crossystem tpm_kernver` to verify kernel version.
Run `flashrom --p internal:bus=spi --wp-status` to verify software WP disabled
Run R11 factory install shim
After install finishes, boot to root shell
Run `crossystem tpm_kernver` to verify kernel version is now 0x00010001

Review URL: http://codereview.chromium.org/6840031

factory_install.sh

diff --git a/factory_install.sh b/factory_install.sh
index fef4779..dc0cb43 100644
--- a/factory_install.sh
+++ b/factory_install.sh
@@ -1,6 +1,6 @@
 #!/bin/sh -ex
 
-# Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+# Copyright (c) 2011 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.
 
@@ -89,9 +89,14 @@
   # Check for physical firmware write protect. We'll only
   # clear this stuff if the case is open.
   if [ "$(crossystem wpsw_cur)" = "0" ]; then
-    # Ensure that flash chips are in a known good state.
+    # Clear software firmware write protect.
     clear_fwwp
+  fi
 
+  # Check for software firmware write protect.  We only clear the TPM if
+  # software write protect is disabled.
+  if flashrom -p internal:bus=spi --wp-status 2>/dev/null |
+      grep -q "write protect is disabled"; then
     # Ensure that we can wipe TPM if necessary.
     clear_tpm
   fi