Introduce TPM_BOARD_CFG register

This patch adds the TPM vendor-defined register, TPM_BOARD_CFG,
which indicates the board configuration status. This register is
attributed as one-time-programmable and the value is maintained
across deep sleeps. Cr50 allows a write on this register right after
a cr50 reset until it receives a TPM2_PCR_Extend command.

BUG=b:148691139
TEST=none

Signed-off-by: Namyoon Woo <namyoon@google.com>
Change-Id: I89ae5a53c15990ef78812aec5da81a59f04d7d98
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2202838
Tested-by: Namyoon Woo <namyoon@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Commit-Queue: Namyoon Woo <namyoon@chromium.org>

2 files changed, 52 insertions, 0 deletions

diff --git a/board/cr50/board.c b/board/cr50/board.c
index 355c92ff97..3c73181cc5 100644
--- a/board/cr50/board.c
+++ b/board/cr50/board.c
@@ -1779,3 +1779,33 @@ int board_nvmem_legacy_check_needed(void)
 
 	return (h->major_ <= 2) || (h->minor_ <= 18);
 }
+
+/*
+ * TPM_BOARD_CFG write is allowed from TPM reset until TPM2_PCR_Extend command
+ * is requested.
+ */
+static bool board_cfg_reg_write_disabled_;
+
+void board_cfg_reg_write_disable(void)
+{
+	board_cfg_reg_write_disabled_ = true;
+}
+
+void board_cfg_reg_write(uint32_t value)
+{
+	/*
+	 * If BIOS requested TPM2_PCR_Extended command already or
+	 * PWRDN_SCRATCH21 is already written, then do not allow the register
+	 * write but return.
+	 */
+	if (GREG32(PMU, PWRDN_SCRATCH21) || board_cfg_reg_write_disabled_)
+		return;
+
+	/* Store the tpm_board_cfg in power-down scratch. */
+	GREG32(PMU, PWRDN_SCRATCH21) = value|BOARD_CFG_LOCKED_BIT;
+}
+
+uint32_t board_cfg_reg_read(void)
+{
+	return GREG32(PMU, PWRDN_SCRATCH21);
+}
diff --git a/board/cr50/board.h b/board/cr50/board.h
index ea0ac15dae..67cd0f7faf 100644
--- a/board/cr50/board.h
+++ b/board/cr50/board.h
@@ -407,6 +407,28 @@ void board_unwedge_i2cs(void);
 
 int board_in_prod_mode(void);
 
+/* Bit masks for each bit in TPM_BOARD_CFG register */
+enum board_cfg_reg_bitmask {
+	BOARD_CFG_LOCKED_BIT = BIT(31),
+};
+
+/* Disable write on TPM_BOARD_CFG register. */
+void board_cfg_reg_write_disable(void);
+
+/*
+ * Write on TPM_BOARD_CFG register if BOARD_CFG_LOCKED_BIT is clear.
+ *
+ * @param value: value to write on TPM_BOARD_CFG
+ */
+void board_cfg_reg_write(unsigned int value);
+
+/*
+ * Read TPM_BOARD_CFG register.
+ *
+ * @param TPM_BOARD_CFG register value in uint32_t type.
+ */
+unsigned int board_cfg_reg_read(void);
+
 #endif /* !__ASSEMBLER__ */
 
 /* USB interface indexes (use define rather than enum to expand them) */