Re: [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@xxxxxxxxxxxxx>
> ---
>  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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