Re: [PATCH v2] clocksource/drivers/nxp-stm: Register sched_clock once

[Juhee Kang]

Hi Daniel,

Just following up on this v2. Ghennadi reviewed and tested the patch.
Could you take a look when you have a chance and let me know
if anything else is needed?

Thanks.

On Thu, Oct 15, 2026 at 8:40 PM Ghennadi Procopciuc
<ghennadi.procopciuc@xxxxxxxxxxx> wrote:
>
> On 10/15/2026 2:37 PM, Juhee Kang wrote:
> > [You don't often get email from juhee.kang@xxxxxxxxxx. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> >
> > Each probe updates stm_sched_clock before calling sched_clock_register()
> > again. The call then subtracts the counter value saved during the
> > previous registration from the new STM's counter. If the new counter is
> > smaller, the subtraction wraps and the timestamp jumps forward.
> > (e.g. from 0.4 to 32.9 seconds below)
> >
> >   [    0.403653] sched_clock: 32 bits at 132MHz, resolution 7ns, wraps every 16243448316ns
> >   [    0.404056] clocksource: timer@40120000: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 14456668980 ns
> >   [   32.890509] sched_clock: 32 bits at 132MHz, resolution 7ns, wraps every 16243448316ns
> >   [   32.890882] clocksource: timer@40124000: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 14456668980 ns
> >
> > To fix this, register sched_clock once at the end of the first
> > successful probe. Clocksource and per-CPU clockevent registration
> > remain unchanged.
> >
> > Fixes: cec32ac75827 ("clocksource/drivers/nxp-timer: Add the System Timer Module for the s32gx platforms")
> > Reported-by: Dustin Black <dblack@xxxxxxxxxx>
> > Signed-off-by: Juhee Kang <juhee.kang@xxxxxxxxxx>
> > Reviewed-by: Ghennadi Procopciuc <ghennadi.procopciuc@xxxxxxxxxxx>
> > ---
> > Changes in v2:
> >   - add the comment
> > ---
> >  drivers/clocksource/timer-nxp-stm.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/clocksource/timer-nxp-stm.c b/drivers/clocksource/timer-nxp-stm.c
> > index 6fe098a4a33f..23b2d44e4b78 100644
> > --- a/drivers/clocksource/timer-nxp-stm.c
> > +++ b/drivers/clocksource/timer-nxp-stm.c
> > @@ -211,10 +211,6 @@ static int nxp_stm_clocksource_init(struct device *dev, struct stm_timer *stm_ti
> >         if (ret)
> >                 return ret;
> >
> > -       stm_sched_clock = stm_timer;
> > -
> > -       sched_clock_register(nxp_stm_read_sched_clock, 32, stm_timer->rate);
> > -
> >         dev_dbg(dev, "Registered clocksource %s\n", name);
> >
> >         return 0;
> > @@ -473,6 +469,15 @@ static int nxp_stm_timer_probe(struct platform_device *pdev)
> >                         return ret;
> >         }
> >
> > +       /*
> > +        * STM counters run independently at the same rate. Use the first
> > +        * probed instance for sched_clock to avoid timestamp jumps.
> > +        */
> > +       if (!stm_sched_clock) {
> > +               stm_sched_clock = stm_timer;
> > +               sched_clock_register(nxp_stm_read_sched_clock, 32, stm_timer->rate);
> > +       }
> > +
> >         return 0;
> >  }
> >
> > --
> > 2.55.0
>
> Thank you for addressing this issue!
>
> Tested-by: Ghennadi Procopciuc <ghennadi.procopciuc@xxxxxxxxxxx>
>
> --
> Regards,
> Ghennadi
>