> -----Original Message-----
> From: Miroslav Lichvar <mlich...@redhat.com>
> Sent: Thursday, October 20, 2022 7:13 AM
> To: linuxptp-devel@lists.sourceforge.net
> Subject: [Linuxptp-devel] [PATCH v2 4/4] Extend clockcheck to check for
> changes
> in frequency.
>
> Before setting the new frequency offset on a clock update, compare the
> current frequency returned by the kernel with the value saved from the
> previous update. Print a warning message if the difference is larger
> than 1 ppb, allowing for rounding errors in conversion to and from
> double. The kernel caches the value set by clock_adjtime() in shifted
> ppm, it doesn't request it from the driver, which can have a lower
> resulution.
>
> This should detect misconfigurations where multiple processes are trying
> to control the clock (e.g. another ptp4l/phc2sys instance or an NTP
> client), even when they don't step the clock.
>
> Signed-off-by: Miroslav Lichvar <mlich...@redhat.com>
> ---
> clock.c | 3 +++
> clockcheck.c | 10 ++++++++++
> clockcheck.h | 8 ++++++++
> phc2sys.c | 3 +++
> ptp4l.8 | 4 +++-
> 5 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/clock.c b/clock.c
> index 46ac9c2..8177e77 100644
> --- a/clock.c
> +++ b/clock.c
> @@ -1776,6 +1776,9 @@ static void clock_step_window(struct clock *c)
>
> static void clock_synchronize_locked(struct clock *c, double adj)
> {
> + if (c->sanity_check) {
> + clockcheck_freq(c->sanity_check, clockadj_get_freq(c->clkid));
> + }
> clockadj_set_freq(c->clkid, -adj);
> if (c->clkid == CLOCK_REALTIME) {
> sysclk_set_sync();
> diff --git a/clockcheck.c b/clockcheck.c
> index f0141be..b5a69cc 100644
> --- a/clockcheck.c
> +++ b/clockcheck.c
> @@ -123,6 +123,16 @@ void clockcheck_set_freq(struct clockcheck *cc, int freq)
> cc->freq_known = 1;
> }
>
> +int clockcheck_freq(struct clockcheck *cc, int freq)
> +{
> + /* Allow difference of 1 ppb due to conversion to/from double */
> + if (cc->freq_known && abs(cc->current_freq - freq) > 1) {
> + pr_warning("clockcheck: clock frequency changed
> unexpectedly!");
The modified documentation would make me think this should allow up to the
sanity_freq_limit as a difference? Perhaps the documentation should be improved
somewhat to clarify the difference?
Thanks,
Jake
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