CBI: Retry read and cache the result

This patch makes read_board_info retry to read CBI on error. The
successive calls will be immediately returned with the cached result.
This will avoid attempting reads doomed to fail.

BUG=b:70294260
BRANCH=none
TEST=ectool cbi get 0

Change-Id: Iacd9cc38bab814af9188c4557c2ee751c421e3a3
Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/872259
Reviewed-by: Randall Spangler <rspangler@chromium.org>

1 files changed, 19 insertions, 12 deletions

diff --git a/common/cbi.c b/common/cbi.c
index 41e8606487..bc21d901fa 100644
--- a/common/cbi.c
+++ b/common/cbi.c
@@ -17,12 +17,9 @@
 #define CPRINTS(format, args...) cprints(CC_SYSTEM, "CBI " format, ## args)
 
 #define EEPROM_PAGE_WRITE_SIZE	16
+#define EC_ERROR_CBI_CACHE_INVALID	EC_ERROR_INTERNAL_FIRST
 static struct board_info bi;
-/* TODO: Init it to -1. On error (I2C or bad contents), retry a read and set it
- * to enum ec_error_list if it still fails. The successive calls can be
- * immediately returned with the cached error code. This will avoid attempting
- * reads doomed to fail. */
-static int initialized;
+static int cached_read_result = EC_ERROR_CBI_CACHE_INVALID;
 
 static uint8_t cbi_crc8(const struct board_info *bi)
 {
@@ -32,14 +29,11 @@ static uint8_t cbi_crc8(const struct board_info *bi)
 /*
  * Get board information from EEPROM
  */
-static int read_board_info(void)
+static int do_read_board_info(void)
 {
 	uint8_t buf[256];
 	uint8_t offset;
 
-	if (initialized)
-		return EC_SUCCESS;
-
 	CPRINTS("Reading board info");
 
 	/* Read header */
@@ -92,11 +86,24 @@ static int read_board_info(void)
 	       sizeof(bi) - sizeof(bi.head));
 	/* If we're handling previous version, clear all new fields */
 
-	initialized = 1;
-
 	return EC_SUCCESS;
 }
 
+static int read_board_info(void)
+{
+	if (cached_read_result != EC_ERROR_CBI_CACHE_INVALID)
+		/* We already tried and know the result. Return the cached
+		 * error code immediately to avoid wasteful reads. */
+		return cached_read_result;
+
+	cached_read_result = do_read_board_info();
+	if (cached_read_result)
+		/* On error (I2C or bad contents), retry a read */
+		cached_read_result = do_read_board_info();
+
+	return cached_read_result;
+}
+
 static int eeprom_is_write_protected(void)
 {
 	return !gpio_get_level(GPIO_WP_L);
@@ -196,7 +203,7 @@ static int hc_cbi_set(struct host_cmd_handler_args *args)
 	if (p->flag & CBI_SET_INIT) {
 		memset(&bi, 0, sizeof(bi));
 		memcpy(&bi.head.magic, cbi_magic, sizeof(cbi_magic));
-		initialized = 1;
+		cached_read_result = EC_SUCCESS;
 	} else {
 		if (read_board_info())
 			return EC_RES_ERROR;