cr50: clear TPM NVMEM cache when entering Alt OS

Each time TPM is disabled for booting Alt OS, NVMEM cache needs to be
wiped out, only a few NV indices need to be preserved.

We also are making sure that wipeout is possible only if key ladder is
disabled.

CQ-DEPEND=CL:1362161
BRANCH=cr50, cr50-mp
BUG=b:119221935
TEST=on a dual boot machine observed that when booting ALT OS on
     reboots, key ladder is disabled, but RW AP firmware rollback
     indices at address 0x1007 are still read properly. Alt OS resume
     happens pretty quickly.

Change-Id: I5326937d0a36b67ac848629faeee42aadcb9e64d
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1362203
Reviewed-by: Andrey Pronin <apronin@chromium.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/board/cr50/tpm2/nvmem_ops.c b/board/cr50/tpm2/nvmem_ops.c
new file mode 100644
index 0000000000..0f2e977967
--- /dev/null
+++ b/board/cr50/tpm2/nvmem_ops.c
@@ -0,0 +1,18 @@
+/* Copyright 2018 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.
+ */
+
+#include "Global.h"
+#include "NV_fp.h"
+
+void nvmem_wipe_cache(void)
+{
+	/*
+	 * Inclusive list of NV indices not to be wiped out when invalidating
+	 * the cache.
+	 */
+	const uint16_t whitelist_range[] = { 0x1007, 0x100b };
+
+	NvSelectivelyInvalidateCache(whitelist_range);
+}