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rtc: Try to prevent RTC errors from accumulating.

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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>
This commit is contained in:
Arve Hjønnevåg 2008-07-25 20:58:15 -07:00
parent d1d79061a9
commit 65a8471259
1 changed files with 11 additions and 2 deletions
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13
drivers/rtc/class.c
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@ -40,25 +40,32 @@ 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;
}
@ -78,6 +85,8 @@ 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));