system: Add generic bbram read / write routines

Add generic routines to read or write a byte to battery-backed RAM, and
implement vbnvcontext get/set using these routines.

BUG=chrome-os-partner:62952
BRANCH=reef
TEST=On reef, with subsequent commit, run "cutoff" on the console,
reattach AC, and verify device successfully wakes. Also verify Rp is
dropped on console 'reboot' and F3 + power from RW.

Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Change-Id: I14691923f2e5198e901b6b5199e92c58c68cd18d
Reviewed-on: https://chromium-review.googlesource.com/444444
Commit-Ready: Shawn N <shawnn@chromium.org>
Tested-by: Shawn N <shawnn@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>

1 files changed, 33 insertions, 22 deletions

diff --git a/chip/stm32/system.c b/chip/stm32/system.c
index d296a90fa5..458b90402f 100644
--- a/chip/stm32/system.c
+++ b/chip/stm32/system.c
@@ -336,36 +336,47 @@ const char *system_get_chip_revision(void)
 	return "";
 }
 
-int system_get_vbnvcontext(uint8_t *block)
+static int bkpdata_index_lookup(enum system_bbram_idx idx, int *msb)
 {
-	enum bkpdata_index i;
-	uint16_t value;
-
-	for (i = BKPDATA_INDEX_VBNV_CONTEXT0;
-			i <= BKPDATA_INDEX_VBNV_CONTEXT7; i++) {
-		value = bkpdata_read(i);
-		*block++ = (uint8_t)(value & 0xff);
-		*block++ = (uint8_t)(value >> 8);
+	*msb = 0;
+
+	if (idx >= SYSTEM_BBRAM_IDX_VBNVBLOCK0 &&
+	    idx <= SYSTEM_BBRAM_IDX_VBNVBLOCK15) {
+		*msb = (idx - SYSTEM_BBRAM_IDX_VBNVBLOCK0) % 2;
+		return BKPDATA_INDEX_VBNV_CONTEXT0 +
+		       (idx - SYSTEM_BBRAM_IDX_VBNVBLOCK0) / 2;
 	}
+	return -1;
+}
+
+int system_get_bbram(enum system_bbram_idx idx, uint8_t *value)
+{
+	int msb = 0;
+	int bkpdata_index = bkpdata_index_lookup(idx, &msb);
+
+	if (bkpdata_index < 0)
+		return EC_ERROR_INVAL;
 
+	*value = (bkpdata_read(bkpdata_index) >> (8 * msb)) & 0xff;
 	return EC_SUCCESS;
 }
 
-int system_set_vbnvcontext(const uint8_t *block)
+int system_set_bbram(enum system_bbram_idx idx, uint8_t value)
 {
-	enum bkpdata_index i;
-	uint16_t value;
-	int err;
-
-	for (i = BKPDATA_INDEX_VBNV_CONTEXT0;
-			i <= BKPDATA_INDEX_VBNV_CONTEXT7; i++) {
-		value = *block++;
-		value |= ((uint16_t)*block++) << 8;
-		err = bkpdata_write(i, value);
-		if (err)
-			return err;
-	}
+	uint16_t read;
+	int msb = 0;
+	int bkpdata_index = bkpdata_index_lookup(idx, &msb);
+
+	if (bkpdata_index < 0)
+		return EC_ERROR_INVAL;
+
+	read = bkpdata_read(bkpdata_index);
+	if (msb)
+		read = (read & 0xff) | (value << 8);
+	else
+		read = (read & 0xff00) | value;
 
+	bkpdata_write(bkpdata_index, read);
 	return EC_SUCCESS;
 }