cr50: Avoiding nvram commits at startup

This patch eliminates NVMEM commits at system startup, namely between
the moment the TPM is reset and the moment the AP is trying to read a
PCR (which is an indication of the AP having booted into OS).

To avoid losing NVMEM changes in case TPM is reset before PCR Read
command is issued, pending changes (if any) are saved before TPM reset
is processed.

For the same reason TPM reset invocation is being added to the hard
reboot path; this will kick in when there is a restart after cr50
firmware update.

BRANCH=none
BUG=chrome-os-partner:59873
TEST=with instrumented coreboot/depthcharge observed the following
     execution times for various TPM command issued at startup

  command 0x144, 15203 us
  command 0x14e, 11814 us
  command 0x182, 12461 us
  command 0x182, 12456 us
  command 0x138, 11503 us
  command 0x138, 11512 us
  command 0x14e, 14648 us
  command 0x14e, 12597 us
  command 0x121, 11353 us

    which totals 113 ms and shaves more than 200 ms off the boot time.

Change-Id: Ic52309291fdb9c3ede96e0ad015ad9fc076bddc5
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/424063
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Andrey Pronin <apronin@chromium.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/board/cr50/board.c b/board/cr50/board.c
index ab3f959a62..229f4ab1f0 100644
--- a/board/cr50/board.c
+++ b/board/cr50/board.c
@@ -403,11 +403,17 @@ void sys_rst_asserted(enum gpio_signal signal)
 		return;
 	}
 
-	if (reboot_request_posted)
+	if (reboot_request_posted) {
+		/*
+		 * Reset TPM and wait to completion to make sure nvmem is
+		 * committed before reboot.
+		 */
+		tpm_reset(1, 0);
 		system_reset(SYSTEM_RESET_HARD);  /* This will never return. */
-
-	/* Re-initialize the TPM software state */
-	tpm_reset(0, 0);
+	} else {
+		/* Reset TPM, no need to wait for completion. */
+		tpm_reset(0, 0);
+	}
 }
 
 void assert_sys_rst(void)