Re: [PATCH v2 5/6] pps: Always use ktime_get_snapshot_id() for pps_get_ts()

[Rodolfo Giometti]

On 06/11/2026 04:08, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
>
> Without CONFIG_NTP_PPS, pps_get_ts() fills in ts_real with
> ktime_get_real_ts64(). Use ktime_get_snapshot_id() unconditionally so
> that PPS timestamps always come from the snapshot machinery; only the
> raw timestamp remains conditional on CONFIG_NTP_PPS.
>
> This is preparation for the next commit, which corrects the snapshot's
> ::systime for the accumulated ntp_error. That correction should reach
> *all* PPS consumers, not only those on CONFIG_NTP_PPS kernels.
>
> The cost of the snapshot on a small ARM board (Cortex-A53, 12.5MHz
> arch counter) is 38.8ns from the pulse handler to the counter read,
> against 23.4ns for ktime_get_real_ts64() — both small against the
> ~2.8µs measured from the pin edge to the handler.
>
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> ---
> v2: New in this series, ahead of the snapshot correction so that its
>     effect explicitly covers all PPS consumers.
>
>  include/linux/pps_kernel.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h
> index 00b840970d56..35d6ac06a0c0 100644
> --- a/include/linux/pps_kernel.h
> +++ b/include/linux/pps_kernel.h
> @@ -100,14 +100,12 @@ static inline void timespec_to_pps_ktime(struct pps_ktime *kt,
>
>  static inline void pps_get_ts(struct pps_event_time *ts)
>  {
> -#ifdef CONFIG_NTP_PPS
>  	struct system_time_snapshot snap;
>
>  	ktime_get_snapshot_id(CLOCK_REALTIME, &snap);
>  	ts->ts_real = ktime_to_timespec64(snap.systime);
> +#ifdef CONFIG_NTP_PPS
>  	ts->ts_raw = ktime_to_timespec64(snap.monoraw);
> -#else
> -	ktime_get_real_ts64(&ts->ts_real);
>  #endif
>  }
>

Acked-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>

Ciao,

Rodolfo

-- 
GNU/Linux Solutions                  e-mail: giometti@xxxxxxxxxxxx
Linux Device Driver                          giometti@xxxxxxxx
Embedded Systems                     phone:  +39 349 2432127
UNIX programming