rtc: Try to prevent RTC errors from accumulating.

When we resume we only know how many whole seconds has elapsed.
These errors would accumulate in delta. We now only set the delta
if it would change by more than two seconds. If we drift back by
by more than a second add one in resume.

Signed-off-by: Arve Hjønnevåg <arve@android.com>

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index c404b61..ec7d9de 100644 (file)
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -42,25 +42,32 @@ static void rtc_device_release(struct device *dev)
  */
 
 static struct timespec delta;
+static struct timespec delta_delta;
 static time_t          oldtime;
 
 static int rtc_suspend(struct device *dev, pm_message_t mesg)
 {
        struct rtc_device       *rtc = to_rtc_device(dev);
        struct rtc_time         tm;
-       struct timespec         ts = current_kernel_time();
+       struct timespec         ts;
+       struct timespec         new_delta;
 
        if (strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)
                return 0;
 
+       getnstimeofday(&ts);
        rtc_read_time(rtc, &tm);
        rtc_tm_to_time(&tm, &oldtime);
 
        /* RTC precision is 1 second; adjust delta for avg 1/2 sec err */
-       set_normalized_timespec(&delta,
+       set_normalized_timespec(&new_delta,
                                ts.tv_sec - oldtime,
                                ts.tv_nsec - (NSEC_PER_SEC >> 1));
 
+       /* prevent 1/2 sec errors from accumulating */
+       delta_delta = timespec_sub(new_delta, delta);
+       if (delta_delta.tv_sec < -2 || delta_delta.tv_sec >= 2)
+               delta = new_delta;
        return 0;
 }
 
@@ -80,6 +87,8 @@ static int rtc_resume(struct device *dev)
                return 0;
        }
        rtc_tm_to_time(&tm, &newtime);
+       if (delta_delta.tv_sec < -1)
+               newtime++;
        if (newtime <= oldtime) {
                if (newtime < oldtime)
                        pr_debug("%s:  time travel!\n", dev_name(&rtc->dev));