linux-kernel - Re: [PATCH v3 1/2] time: Don't bother to run rtc

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Date:	Wed, 11 Feb 2015 14:52:57 +0800
From:	Xunlei Pang <pang.xunlei@...aro.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Xunlei Pang <xlpang@....com>, lkml <linux-kernel@...r.kernel.org>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Arnd Bergmann <arnd.bergmann@...aro.org>
Subject: Re: [PATCH v3 1/2] time: Don't bother to run rtc_resume() for the
 nonstop clocksource

Hi John,

On 11 February 2015 at 08:01, John Stultz <john.stultz@...aro.org> wrote:
> On Thu, Jan 29, 2015 at 11:59 PM, Xunlei Pang <xlpang@....com> wrote:
>> From: Xunlei Pang <pang.xunlei@...aro.org>
>>
>> If a system does not provide a persistent_clock(), the time
>> will be updated on resume by rtc_resume(). With the addition
>> of the non-stop clocksources for suspend timing, those systems
>> set the time on resume in timekeeping_resume(), but may not
>> provide a valid persistent_clock().
>>
>> This results in the rtc_resume() logic thinking no one has set
>> the time and it then will over-write the suspend time again,
>> which is not necessary and only increases clock error.
>>
>> So, fix this for rtc_resume().
>>
>> Signed-off-by: Xunlei Pang <pang.xunlei@...aro.org>
>> ---
>> v2->v3:
>> Refine according to John's comments using internal variable.
>>
>>  drivers/rtc/class.c         |  2 +-
>>  include/linux/timekeeping.h |  1 +
>>  kernel/time/timekeeping.c   | 32 ++++++++++++++++++++------------
>>  3 files changed, 22 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
>> index 472a5ad..6100af5 100644
>> --- a/drivers/rtc/class.c
>> +++ b/drivers/rtc/class.c
>> @@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
>>         struct timespec64       sleep_time;
>>         int err;
>>
>> -       if (has_persistent_clock())
>> +       if (timekeeping_sleeptime_injected())
>>                 return 0;
>
> Took a closer look here.. So you're replacing has_persistent_clock()
> in the resume side, but not the suspend... Can we not cleanup
> has_persistent_clock and consolidate to one accessor for both sides of
> the suspend?

The sequential calls when the system is suspended are:
rtc_suspend(), then timekeeping_suspend().

The sequential calls when the system is resumed are:
timekeeping_resume(), then rtc_resume().

Obviously, timekeeping_sleeptime_injected() used by rtc_resume()
can be easily determined at timekeeping_resume().

And for nonstop clocksources, currently we have code below:
timekeeping_resume():
cycle_now = tk->tkr.read(clock);
    if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
        cycle_now > tk->tkr.cycle_last) {

Here comes the confusing thing: "cycle_now > tk->tkr.cycle_last".
I can't quite catch what's the purpose by judging cycle_now and cycle_last here,
May Nonstop clocksource get wrapped or still can get disfunctional during
system suspend? If so, I think it would be hard to judge exactly whether
rtc_suspend() is needed for nonstop clocksource cases.

If we can get rid of this judgement, I think it would be easy to
consolidate this just
using read_persistent_clock() and CLOCK_SOURCE_SUSPEND_NONSTOP flag.

Any suggestion for this?

Thanks,
Xunlei

>
>>
>>         rtc_hctosys_ret = -ENODEV;
>> diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
>> index 9b63d13..17a460d 100644
>> --- a/include/linux/timekeeping.h
>> +++ b/include/linux/timekeeping.h
>> @@ -225,6 +225,7 @@ static inline void timekeeping_clocktai(struct timespec *ts)
>>  /*
>>   * RTC specific
>>   */
>> +extern bool timekeeping_sleeptime_injected(void);
>>  extern void timekeeping_inject_sleeptime64(struct timespec64 *delta);
>>
>>  /*
>> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
>> index 6a93185..b02133e 100644
>> --- a/kernel/time/timekeeping.c
>> +++ b/kernel/time/timekeeping.c
>> @@ -1125,12 +1125,26 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
>>         tk_debug_account_sleep_time(delta);
>>  }
>>
>> +static bool sleeptime_inject;
>> +
>> +#if defined(CONFIG_RTC_CLASS) && \
>> +       defined(CONFIG_PM_SLEEP) && \
>> +       defined(CONFIG_RTC_HCTOSYS_DEVICE)
>
> This change wasn't explained in the commit message. Its fine as a
> small optimization, but probably should be split into its own patch.
>
> thanks
> -john
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