[PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

[PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

[Xiubo Li]

The third parameter(u64 start_tstamp) of timecounter_init() should
be the start time by ns, not a cycle counter.

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
---
 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);
-- 
1.8.5

[PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

[Stephen Boyd]

On 06/11/14 01:37, Xiubo Li wrote:
> The third parameter(u64 start_tstamp) of timecounter_init() should
> be the start time by ns, not a cycle counter.
>
> Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
> ---
>  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. Perhaps it would be better to just do

    timecounter_init(&timecounter, &cyclecounter, 0);

or

    timecounter_init(&timecounter, &cyclecounter,
ktime_to_ns(ktime_get_real()));

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hosted by The Linux Foundation

[PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

[Li.Xiubo at freescale.com]

> >  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

[PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

[Stephen Boyd]

On 06/12/14 00:45, Li.Xiubo at freescale.com wrote:
>
> And if so, why not just set it to 0 ? And by the way, 0 is must here ?
>
>

I would just set it to 0 and be done with it. But all of this doesn't
seem very urgent. The only user of this timecounter is using it for the
read() and mult/shift members. We never call timecounter_read() or
timecounter_cyc2time() so the nsec member is irrelevant.

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