Messages in this thread | | | Date | Fri, 14 Jun 2013 20:05:25 +0200 | From | Alexander Holler <> | Subject | Re: [rtc-linux] Re: [PATCH 4/9 RESEND] RFC: timekeeping: introduce flag systime_was_set |
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Am 14.06.2013 19:41, schrieb John Stultz: > On 06/14/2013 09:52 AM, Alexander Holler wrote: >> In order to let an RTC set the time at boot without the problem that a >> second RTC overwrites it, the flag systime_was_set is introduced. >> >> systime_was_set will be true, if a persistent clock sets the time at >> boot, >> or if do_settimeofday() is called (e.g. by the RTC subsystem or >> userspace). >> >> Signed-off-by: Alexander Holler <holler@ahsoftware.de> >> --- >> include/linux/time.h | 6 ++++++ >> kernel/time/timekeeping.c | 10 +++++++++- >> 2 files changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/time.h b/include/linux/time.h >> index d5d229b..888280f 100644 >> --- a/include/linux/time.h >> +++ b/include/linux/time.h >> @@ -129,6 +129,12 @@ extern int update_persistent_clock(struct >> timespec now); >> void timekeeping_init(void); >> extern int timekeeping_suspended; >> +/* >> + * Will be true if the system time was set at least once by >> + * a persistent clock, RTC or userspace. >> + */ >> +extern bool systime_was_set; >> + > > Probably should make this static to timekeeping.c and create an accessor > function so you don't have to export locking rules on this. > > >> unsigned long get_seconds(void); >> struct timespec current_kernel_time(void); >> struct timespec __current_kernel_time(void); /* does not take >> xtime_lock */ >> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c >> index baeeb5c..07d8531 100644 >> --- a/kernel/time/timekeeping.c >> +++ b/kernel/time/timekeeping.c >> @@ -37,6 +37,9 @@ int __read_mostly timekeeping_suspended; >> /* Flag for if there is a persistent clock on this platform */ >> bool __read_mostly persistent_clock_exist = false; >> +/* Flag for if the system time was set at least once */ >> +bool __read_mostly systime_was_set; >> + > Probably should also move this to be part of the timekeeper structure > (since it will be protected by the timekeeper lock. >
I wanted to avoid locks for this silly flag at all. It is only set once at boot (and resume) and set to 0 at suspend. And I don't see any possible race condition which could make a lock necessary. Therefor I've decided to not use a lock or atomic_* in order to skip any delay in setting the time.
Of course, I might be wrong and there might be a use case where multiple things do set the system time concurrently and nothing else did set system time before, but I found that extremly unlikely.
>> static inline void tk_normalize_xtime(struct timekeeper *tk) >> { >> while (tk->xtime_nsec >= ((u64)NSEC_PER_SEC << tk->shift)) { >> @@ -498,6 +501,9 @@ int do_settimeofday(const struct timespec *tv) >> raw_spin_lock_irqsave(&timekeeper_lock, flags); >> write_seqcount_begin(&timekeeper_seq); >> + systime_was_set = true; >> + >> + >> timekeeping_forward_now(tk); >> xt = tk_xtime(tk); > > Might also want to add the flag to inject_offset as well, since that > could be used to set the time.
I wasn't sure about that because I had only a quick look at inject_offset() and had the impression it's only able to inject a relative small offset (so not usable at boot). And, as written sometimes before, I haven't had a deep look at suspend/resume, which might be the only place where it is really used to set the clock when systime_was_set is false.
Regards,
Alexander
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