RE: [PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

Li.Xiubo
2014-06-12T07:45:42Z

> > drivers/clocksource/arm_arch_timer.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/clocksource/arm_arch_timer.c
> b/drivers/clocksource/arm_arch_timer.c
> > index 5163ec1..6c3cfd8 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -426,7 +426,7 @@ struct timecounter *arch_timer_get_timecounter(void)
> >
> > static void __init arch_counter_register(unsigned type)
> > {
> > - u64 start_count;
> > + u64 start_count, start_ns;
> >
> > /* Register the CP15 based counter if we have one */
> > if (type & ARCH_CP15_TIMER)
> > @@ -438,7 +438,8 @@ static void __init arch_counter_register(unsigned type)
> > clocksource_register_hz(&clocksource_counter, arch_timer_rate);
> > cyclecounter.mult = clocksource_counter.mult;
> > cyclecounter.shift = clocksource_counter.shift;
> > - timecounter_init(&timecounter, &cyclecounter, start_count);
> > + start_ns = cyclecounter_cyc2ns(&cyclecounter, start_count);
> > + timecounter_init(&timecounter, &cyclecounter, start_ns);
> >
> > /* 56 bits minimum, so we assume worst case rollover */
> > sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
>
> This doesn't make much sense. We're converting start_count, which could
> be a very large number, into nanoseconds. It looks like we're assuming
> the counter always starts at 0 which is not always true if you sit in a
> bootloader for a long time.

Yes, the counter here may usually start counting at bootloader time from zero.

> Perhaps it would be better to just do
>
> timecounter_init(&timecounter, &cyclecounter, 0);
>
> or
>
> timecounter_init(&timecounter, &cyclecounter,
> ktime_to_ns(ktime_get_real()));
>

Here the ktime_get_real() will always return 0, before setting the system clock,
Like:

"rtc-ds3232 1-0068: setting system clock to 2014-06-12 13:01:24 UTC (1402578084)"

And if so, why not just set it to 0 ? And by the way, 0 is must here ?

Thanks,
BRs
Xiubo