Re: [PATCH] powerpc/time: set ->min_delta_ticks and ->max_delta_ticks

Michael Ellerman
2017-03-31T03:03:30Z

Nicolai Stange <nicstange@gmail.com> writes:

> In preparation for making the clockevents core NTP correction aware,
> all clockevent device drivers must set ->min_delta_ticks and
> ->max_delta_ticks rather than ->min_delta_ns and ->max_delta_ns: a
> clockevent device's rate is going to change dynamically and thus, the
> ratio of ns to ticks ceases to stay invariant.
>
> Make the powerpc arch's clockevent driver initialize these fields properly.
>
> This patch alone doesn't introduce any change in functionality as the
> clockevents core still looks exclusively at the (untouched) ->min_delta_ns
> and ->max_delta_ns. As soon as this has changed, a followup patch will
> purge the initialization of ->min_delta_ns and ->max_delta_ns from this
> driver.
>
> Signed-off-by: Nicolai Stange <nicstange@gmail.com>
> ---
>
> Notes:
> This prerequisite patch is part of a larger effort to feed NTP
> corrections into the clockevent devices' frequencies and thus
> avoiding their notion of time to diverge from the system's
> one. If you're interested, the current state of the whole series
> can be found at [1].
>
> If you haven't got any objections and these prerequisites get
> merged by 4.12 everywhere, I'll proceed with the remainder of
> this series in 4.13.
>
> Applicable to next-20170324 as well as to John' Stultz tree [2].
>
> [1]
> git://nicst.de/linux.git cev-freq-adj.v10.fortglx-4.12-time
> https://nicst.de/git/?p=linux.git;a=shortlog;h=refs/heads/cev-freq-adj.v10.fortglx-4.12-time
>
> [2]
> https://git.linaro.org/people/john.stultz/linux.git fortglx/4.12/time
>
> arch/powerpc/kernel/time.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index 07b90725855e..2b33cfaac7b8 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -995,8 +995,10 @@ static void __init init_decrementer_clockevent(void)
>
> decrementer_clockevent.max_delta_ns =
> clockevent_delta2ns(decrementer_max, &decrementer_clockevent);
> + decrementer_clockevent.max_delta_ticks = decrementer_max;
> decrementer_clockevent.min_delta_ns =
> clockevent_delta2ns(2, &decrementer_clockevent);
> + decrementer_clockevent.min_delta_ticks = 2;

Seems to do what it says on the tin.

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers