cr50: reset only the TPM state on SYS_RST_L

Rather than doing a full cr50 reset when the system reset SYS_RST_L is
asserted, just reset the state of the TPM task and library.  Re-clear
.bss for those modules, then re-initialize.

BRANCH=none
BUG=chrome-os-partner:52366
CQ-DEPEND=CL:366792
TEST=make buildall; test on Gru

Trigger a SYS_RST_L by using the AP's reboot command, power
off/on, log in/out/in.

See that the Cr50 does not reboot and the firmware and userspace
are still happy about the TPM.

Change-Id: I32cd2bb72316f68c74db77a20a8d09112b402d4b
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/361680

8 files changed, 76 insertions, 4 deletions

diff --git a/board/cr50/board.c b/board/cr50/board.c
index 3f365350da..31a8d2fef1 100644
--- a/board/cr50/board.c
+++ b/board/cr50/board.c
@@ -394,8 +394,8 @@ void sys_rst_asserted(enum gpio_signal signal)
 	if (usb_spi_update_in_progress() || is_sys_rst_asserted())
 		return;
 
-	cflush();
-	system_reset(0);
+	/* Re-initialize the TPM software state */
+	task_set_event(TASK_ID_TPM, TPM_EVENT_RESET, 0);
 }
 
 void assert_sys_rst(void)
diff --git a/board/cr50/board.h b/board/cr50/board.h
index 7d11abd60d..cc7589e750 100644
--- a/board/cr50/board.h
+++ b/board/cr50/board.h
@@ -136,6 +136,9 @@ void assert_ec_rst(void);
 void deassert_ec_rst(void);
 int is_ec_rst_asserted(void);
 
+/* Event to request a reset/re-initialization of the TPM task */
+#define TPM_EVENT_RESET (TASK_EVENT_CUSTOM(1))
+
 #endif /* !__ASSEMBLER__ */
 
 /* USB interface indexes (use define rather than enum to expand them) */
diff --git a/board/cr50/build.mk b/board/cr50/build.mk
index f7cc0370b6..6028e34de2 100644
--- a/board/cr50/build.mk
+++ b/board/cr50/build.mk
@@ -79,6 +79,6 @@ $(out)/RW/ec.RW.elf $(out)/RW/ec.RW_B.elf: $(out)/tpm2/libtpm2.a
 # Force the external build each time, so it can look for changed sources.
 .PHONY: $(out)/tpm2/libtpm2.a
 $(out)/tpm2/libtpm2.a:
-	$(MAKE) obj=$(realpath $(out))/tpm2 EMBEDDED_MODE=1 -C $(EXTLIB)
+	$(MAKE) obj=$(realpath $(out))/tpm2 EMBEDDED_MODE=1 OBJ_PREFIX=Tpm2_ -C $(EXTLIB)
 
 endif   # BOARD_MK_INCLUDED_ONCE is nonempty
diff --git a/chip/g/sps_tpm.c b/chip/g/sps_tpm.c
index 2c3f6876e7..3ef12994e6 100644
--- a/chip/g/sps_tpm.c
+++ b/chip/g/sps_tpm.c
@@ -271,3 +271,12 @@ void sps_tpm_enable(void)
 	sps_register_rx_handler(SPS_GENERIC_MODE, tpm_rx_handler, 3);
 	init_new_cycle();
 }
+
+void sps_tpm_disable(void)
+{
+	sps_tpm_state = SPS_TPM_STATE_PONDERING;
+	sps_unregister_rx_handler();
+	/* We don't care anymore, so we can sleep whenever */
+	delay_sleep_by(0);
+	enable_sleep(SLEEP_MASK_SPI);
+}
diff --git a/common/tpm_registers.c b/common/tpm_registers.c
index 2f656096aa..6fcd6eb839 100644
--- a/common/tpm_registers.c
+++ b/common/tpm_registers.c
@@ -12,6 +12,7 @@
 #include "byteorder.h"
 #include "console.h"
 #include "extension.h"
+#include "link_defs.h"
 #include "nvmem.h"
 #include "printf.h"
 #include "signed_header.h"
@@ -493,6 +494,9 @@ void tpm_register_get(uint32_t regaddr, uint8_t *dest, uint32_t data_size)
 
 static void tpm_init(void)
 {
+	/* This is more related to TPM task activity than TPM transactions */
+	cprints(CC_TASK, "%s", __func__);
+
 	set_tpm_state(tpm_state_idle);
 	tpm_.regs.access = tpm_reg_valid_sts;
 	/*
@@ -566,6 +570,33 @@ static void call_extension_command(struct tpm_cmd_header *tpmh,
 }
 #endif
 
+static void tpm_reset(void)
+{
+	/* This is more related to TPM task activity than TPM transactions */
+	cprints(CC_TASK, "%s", __func__);
+
+	sps_tpm_disable();
+
+	/*
+	 * Clear the TPM library's zero-init data.  Note that the linker script
+	 * includes this file's .bss in the same section, so it will be cleared
+	 * at the same time.
+	 */
+	memset(__bss_libtpm2_start, __bss_libtpm2_end - __bss_libtpm2_start, 0);
+
+	/*
+	 * TPM reset currently only clears BSS for the TPM library.  It does
+	 * not reset any initialized variables in data.  So, make sure there
+	 * aren't any.
+	 */
+	ASSERT(__data_libtpm2_start == __data_libtpm2_end);
+
+	/* Re-initialize our registers */
+	tpm_init();
+
+	sps_tpm_enable();
+}
+
 void tpm_task(void)
 {
 	if (system_rolling_reboot_suspected())
@@ -578,9 +609,14 @@ void tpm_task(void)
 		unsigned response_size;
 		uint32_t command_code;
 		struct tpm_cmd_header *tpmh;
+		uint32_t evt;
 
 		/* Wait for the next command event */
-		task_wait_event(-1);
+		evt = task_wait_event(-1);
+		if (evt & TPM_EVENT_RESET) {
+			tpm_reset();
+			continue;
+		}
 		tpmh = (struct tpm_cmd_header *)tpm_.regs.data_fifo;
 		command_code = be32toh(tpmh->command_code);
 		CPRINTF("%s: received fifo command 0x%04x\n",
diff --git a/core/cortex-m/ec.lds.S b/core/cortex-m/ec.lds.S
index 2b70535fa6..5b756cec58 100644
--- a/core/cortex-m/ec.lds.S
+++ b/core/cortex-m/ec.lds.S
@@ -243,6 +243,14 @@ SECTIONS
         . = ALIGN(8);
         *(.bss.system_stack)
 	/* Rest of .bss takes care of its own alignment */
+
+	/* Group libtpm2 data so it can be cleared on system reset */
+	__bss_libtpm2_start = .;
+	Tpm2_*(.bss)
+	/* TPM registers should be cleared at the same time */
+        STRINGIFY(OUTDIR/common/tpm_registers.o*)(.bss)
+	__bss_libtpm2_end = .;
+
         *(.bss)
 
 	/*
@@ -284,6 +292,14 @@ SECTIONS
         . = ALIGN(4);
         __data_start = .;
         *(.data.tasks)
+
+	/* Group libtpm2 data so it can be reinitialized on system reset */
+	__data_libtpm2_start = .;
+	Tpm2_*(.data)
+	/* TPM registers should be reinitialized at the same time */
+        STRINGIFY(OUTDIR/common/tpm_registers.o*)(.data)
+	__data_libtpm2_end = .;
+
         *(.data)
 #ifdef CONFIG_MPU
         /* It has to be aligned by 32 bytes to be a valid MPU region. */
diff --git a/include/link_defs.h b/include/link_defs.h
index 69b964d1d8..e55da8bd50 100644
--- a/include/link_defs.h
+++ b/include/link_defs.h
@@ -87,6 +87,12 @@ extern const void *__irqhandler[];
 /* Shared memory buffer.  Use via shared_mem.h interface. */
 extern uint8_t __shared_mem_buf[];
 
+/* Image sections used by the TPM2 library */
+extern uint8_t *__bss_libtpm2_start;
+extern uint8_t *__bss_libtpm2_end;
+extern uint8_t *__data_libtpm2_start;
+extern uint8_t *__data_libtpm2_end;
+
 /* Image sections. */
 extern const void *__ro_end;
 extern const void *__data_start;
diff --git a/include/tpm_registers.h b/include/tpm_registers.h
index 3416492f03..35f6dff471 100644
--- a/include/tpm_registers.h
+++ b/include/tpm_registers.h
@@ -25,6 +25,8 @@ void tpm_register_get(uint32_t regaddr, uint8_t *dest, uint32_t data_size);
 
 /* Enable SPS TPM driver. */
 void sps_tpm_enable(void);
+/* Disable SPS TPM driver. */
+void sps_tpm_disable(void);
 
 /* Get the current value of the burst size field of the status register. */
 size_t tpm_get_burst_size(void);