HACK tpm: reset fallback counter when ready

As a temp measure until a proper solution is implemented, reset the
restart counter when the PCR_Read command is issued by the host.

This is a good indication that Chrome OS is through the boot process,
as PCR value is used to determine the boot mode.

BRANCH=none
BUG=chrome-os-partner:55667
TEST=installed the new image on a Kevin cr50 and rebooted it in normal
     and recovery modes, observed on the cr50 console the message like
  > system_process_retry_counter:retry counter 1

Change-Id: Ib55e161d5edbf8f6e2d387fd756b94aa53c20ed8
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/364311
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

chip/g/system.c

@@ -323,11 +323,11 @@ int system_process_retry_counter(void)
 	GREG32(PMU, LONG_LIFE_SCRATCH0) = 0;
 	GWRITE_FIELD(PMU, LONG_LIFE_SCRATCH_WR_EN, REG0, 0);
 
+	ccprintf("%s:retry counter %d\n", __func__, retry_counter);
+
 	if (retry_counter <= RW_BOOT_MAX_RETRY_COUNT)
 		return EC_SUCCESS;
 
-	ccprintf("%s:retry counter %d\n", __func__, retry_counter);
-
 	if (system_get_image_copy() == SYSTEM_IMAGE_RW) {
 		me = (struct SignedHeader *)
 			get_program_memory_addr(SYSTEM_IMAGE_RW);

common/tpm_registers.c

@@ -568,6 +568,12 @@ void tpm_task(void)
 		CPRINTF("got %d bytes in response\n", response_size);
 		if (response_size &&
 		    (response_size <= sizeof(tpm_.regs.data_fifo))) {
+			/*
+			 * TODO(vbendeb): revisit this when
+			 * crosbug.com/p/55667 has been addressed.
+			 */
+			if (command_code == TPM2_PCR_Read)
+				system_process_retry_counter();
 #ifdef CONFIG_EXTENSION_COMMAND
 			if (command_code != CONFIG_EXTENSION_COMMAND)
 #endif

include/system.h

@@ -458,4 +458,12 @@ uintptr_t system_get_fw_reset_vector(uintptr_t base);
  */
 int system_is_reboot_warm(void);
 
+/**
+ * On systems with protection from a failing RW update: read the retry counter
+ * and act on it.
+ *
+ * @return EC_SUCCESS if no flash write errors were encounterd.
+ */
+int system_process_retry_counter(void);
+
 #endif  /* __CROS_EC_SYSTEM_H */

include/tpm_registers.h

@@ -40,4 +40,10 @@ struct tpm_cmd_header {
 	uint16_t subcommand_code;  /* Not a standard field. */
 } __packed;
 
+/*
+ * The only TPM2 command we care about on the driver level, see
+ * crosbug.com/p/55667 for detals.
+ */
+#define TPM2_PCR_Read		0x0000017e
+
 #endif	/* __CROS_EC_TPM_REGISTERS_H */