Subject: [PATCH V2] ARM: OMAP: counter: add locking to read_persistent_clock

From: [email-masked] (Tony Lindgren)
Date: Tue, 25 Sep 2012 08:17:55 -0700

* R, Sricharan <[email-masked]> [120925 00:44]:
> Hi Tony,
> 
> [snip..]
> 
> >> > index dbf1e03..2bc51fb 100644
> >> > --- a/arch/arm/plat-omap/counter_32k.c
> >> > +++ b/arch/arm/plat-omap/counter_32k.c
> >> > @@ -55,22 +55,29 @@ static u32 notrace omap_32k_read_sched_clock(void)
> >> >   * nsecs and adds to a monotonically increasing timespec.
> >> >   */
> >> >  static struct timespec persistent_ts;
> >> > -static cycles_t cycles, last_cycles;
> >> > +static cycles_t cycles;
> >> >  static unsigned int persistent_mult, persistent_shift;
> >> > +static DEFINE_SPINLOCK(read_persistent_clock_lock);
> >> > +
> >> >  static void omap_read_persistent_clock(struct timespec *ts)
> >> >  {
> >> >     unsigned long long nsecs;
> >> > -   cycles_t delta;
> >> > -   struct timespec *tsp = &persistent_ts;
> >> > +   cycles_t last_cycles;
> >> > +   unsigned long flags;
> >> > +
> >> > +   spin_lock_irqsave(&read_persistent_clock_lock, flags);
> >> >
> >> >     last_cycles = cycles;
> >> >     cycles = sync32k_cnt_reg ? __raw_readl(sync32k_cnt_reg) : 0;
> >> > -   delta = cycles - last_cycles;
> >> >
> >> > -   nsecs = clocksource_cyc2ns(delta, persistent_mult, persistent_shift);
> >> > +   nsecs = clocksource_cyc2ns(cycles - last_cycles,
> >> > +                                   persistent_mult, persistent_shift);
> >
> > ..I think there's another bug here where cycles - last_cycles
> > returns wrong value when the timer wraps around as cycles_t is
> > 64 bits and the counter is 32 bits. It seems it's been there
> > since when the read_persistent_clock was added with commit
> > d92cfcbe (OMAP: timekeeping: time should not stop during suspend)?
> >
> > It seems that after this patch cycles should not be cycles_t
> > but u32, and the result of cycles - last_cycles should also
> > be u32.
> >
>  cycles_t is defined as  typedef unsigned long cycles_t;
>  Am i missing something here ?

Oh right, cycles_t is unsigned long, it's OK then. Must
have grepped for it from some other arch.

Regards,

Tony