npcx: Don't clear IBBR bit via a read-modify-write sequence

In npcx5/npcx7m6g/npcx7m6f, clearing the IBBR bit in the BKUP_STS
register is not hazardous because the register only implements the IBBR
bit. In npcx7m6fb/npcx7m7wb, the register implements two more bits
(VSBY_STS/VCC1_STS). Using read-modify-write operation to clear IBBR bit
will also clear these two bits unexpected if they are set. It is fine at
this time because the firmware does not rely on these two new bits for
any purpose. But it will be better to change it in case these two bits
are used in the future.

This CL also clears VSBY_STS/VCC1_STS bit (for npcx7m6fb/npcx7m7wb) when
power-on reset.

BRANCH=none
BUG=none
TEST=No build error for make buildall; Check IBBR(VSBY_STS/VCC1_STS)
are cleared at initial when power-on reset. Check warining messages are
printed and IBBR bit is cleared (in function system_check_bbram_on_reset
and bbram_valid).

Change-Id: I6dc1f5d7f35f9d591db62d1b022ea7b8d92f5b92
Signed-off-by: CHLin <CHLIN56@nuvoton.com>
Reviewed-on: https://chromium-review.googlesource.com/1235733
Commit-Ready: CH Lin <chlin56@nuvoton.com>
Tested-by: CH Lin <chlin56@nuvoton.com>
Reviewed-by: Jonathan Brandmeyer <jbrandmeyer@chromium.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/chip/npcx/system.c b/chip/npcx/system.c
index a286090bd8..edfbcf455b 100644
--- a/chip/npcx/system.c
+++ b/chip/npcx/system.c
@@ -98,8 +98,11 @@ void system_check_bbram_on_reset(void)
 			IS_BIT_SET(NPCX_RSTCTL, NPCX_RSTCTL_VCC1_RST_STS))
 			CPRINTF("VBAT drop!\n");
 
-		/* Clear IBBR bit */
-		SET_BIT(NPCX_BKUP_STS, NPCX_BKUP_STS_IBBR);
+		/*
+		 * npcx5/npcx7m6g/npcx7m6f - Clear IBBR bit
+		 * npcx7m6fb/npcx7m7wb - Clear IBBR/VSBY_STS/VCC1_STS bit
+		 */
+		NPCX_BKUP_STS = NPCX_BKUP_STS_ALL_MASK;
 	}
 }
 
@@ -112,7 +115,7 @@ static int bbram_valid(enum bbram_data_index index, int bytes)
 
 	/* Check BBRAM is valid */
 	if (IS_BIT_SET(NPCX_BKUP_STS, NPCX_BKUP_STS_IBBR)) {
-		SET_BIT(NPCX_BKUP_STS, NPCX_BKUP_STS_IBBR);
+		NPCX_BKUP_STS = (1 << NPCX_BKUP_STS_IBBR);
 		panic_printf("IBBR set: BBRAM corrupted!\n");
 		return 0;
 	}