linux-kernel - Re: [PATCH 4/9 RESEND] RFC: timekeeping: introduce flag systime_was

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Message-ID: <51BB55C0.7090603@linaro.org>
Date:	Fri, 14 Jun 2013 10:41:20 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Alexander Holler <holler@...oftware.de>
CC:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	rtc-linux@...glegroups.com, Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH 4/9 RESEND] RFC: timekeeping: introduce flag systime_was_set

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@...oftware.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.

>   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.


thanks
-john

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