[U-Boot] [PATCH v5 06/11] rtc: Improve rtc_get() on s3c24x0_rtc

[José Miguel Gonçalves]

A better approach to avoid reading the RTC during updates, as sugested in
the S3C2416 User's Manual.

Signed-off-by: José Miguel Gonçalves <jose.goncalves at inov.pt>
---
Changes for v2:
   - New patch

Changes for v3:
   - Removed unneeded parenthesis

Changes for v4:
   - None

Changes for v5:
   - None
---
 drivers/rtc/s3c24x0_rtc.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/s3c24x0_rtc.c b/drivers/rtc/s3c24x0_rtc.c
index c16ff2e..b31dc53 100644
--- a/drivers/rtc/s3c24x0_rtc.c
+++ b/drivers/rtc/s3c24x0_rtc.c
@@ -65,20 +65,26 @@ int rtc_get(struct rtc_time *tmp)
 	uchar sec, min, hour, mday, wday, mon, year;
 	__maybe_unused uchar a_sec, a_min, a_hour, a_date,
 			     a_mon, a_year, a_armed;
+	int have_retried = 0;
 
 	/* enable access to RTC registers */
 	SetRTC_Access(RTC_ENABLE);
 
 	/* read RTC registers */
 	do {
-		sec  = readb(&rtc->bcdsec);
 		min  = readb(&rtc->bcdmin);
 		hour = readb(&rtc->bcdhour);
 		mday = readb(&rtc->bcddate);
 		wday = readb(&rtc->bcdday);
 		mon  = readb(&rtc->bcdmon);
 		year = readb(&rtc->bcdyear);
-	} while (sec != readb(&rtc->bcdsec));
+		sec  = readb(&rtc->bcdsec);
+		/*
+		 * The only way to work out whether the RTC was mid-update
+		 * when we read it is to check the seconds counter.
+		 * If it's zero, then we re-try the entire read.
+		 */
+	} while (sec == 0 && !have_retried++);
 
 	/* read ALARM registers */
 	a_sec   = readb(&rtc->almsec);
-- 
1.7.9.5