2011/4/29 John Stultz <john.stultz@xxxxxxxxxx>:
> On Fri, 2011-04-29 at 16:28 -0700, Arve Hjønnevåg wrote:
>> On Fri, Apr 29, 2011 at 10:31 AM, tip-bot for John Stultz
>> > @@ -85,15 +82,13 @@ static int rtc_resume(struct device *dev)
>> > pr_debug("%s: time travel!\n", dev_name(&rtc->dev));
>> > return 0;
>> > }
>> > + /* calculate the RTC time delta */
>> > + set_normalized_timespec(&time, newtime - oldtime, 0);
>> >
>> > - /* restore wall clock using delta against this RTC;
>> > - * adjust again for avg 1/2 second RTC sampling error
>> > - */
>> > - set_normalized_timespec(&time,
>> > - newtime + delta.tv_sec,
>> > - (NSEC_PER_SEC >> 1) + delta.tv_nsec);
>> > - do_settimeofday(&time);
>> > + /* subtract kernel time between rtc_suspend to rtc_resume */
>> > + time = timespec_sub(time, timespec_sub(newts, oldts));
>>
>> The delta you got from the rtc can be almost a second to long or
>> short. Do you do anything to prevent these errors from accumulating?
>
> Indeed. Right now we don't do anything.
>
> I'm hoping to extend the RTC interface to provide finer resolution where
> possible, but that won't help on hardware that really only gives us
> seconds.
>
> We could maybe not only track the suspend time but the RTC time deltas
> for when the system is running as well and utilize those values to avoid
> accumulating the error long term. But then there can be other
> complications between the NTP corrected system time and the uncorrected
> RTC time.
>
> Other ideas? I know you've got a patch in the Android tree to try to
> address this, should I try to adapt it for use here?
>
Unless you can make the generic code handle this (in case
read_persistent_clock has the same problem), then I would recommend
adapting that patch to your new rtc code. We have not noticed the
problem after applying that patch.
--
Arve Hjønnevåg
--
To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
|