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

[Tony Lindgren <tony@atomide.com>]

* Tony Lindgren <tony@atomide.com> [120925 08:19]:
> * R, Sricharan <r.sricharan@ti.com> [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.

Applying to fixes with Cc stable.

Regards,

Tony