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

Stephen Boyd
2014-06-11T19:02:14Z

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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