> -----Original Message-----
> From: Andy Shevchenko <[email protected]>
> Sent: Tuesday, April 30, 2024 7:23 PM
> To: D, Lakshmi Sowjanya <[email protected]>
> Cc: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; intel-wired-
> [email protected]; Dong, Eddie <[email protected]>; Hall, Christopher
> S <[email protected]>; Brandeburg, Jesse
> <[email protected]>; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected]; linux-
> [email protected]; Nguyen, Anthony L <[email protected]>;
> [email protected]; N, Pandith <[email protected]>; Mohan,
> Subramanian <[email protected]>; T R, Thejesh Reddy
> <[email protected]>
> Subject: Re: [PATCH v7 10/12] pps: generators: Add PPS Generator TIO Driver
>
> On Tue, Apr 30, 2024 at 02:22:23PM +0530, [email protected]
> wrote:
> > From: Lakshmi Sowjanya D <[email protected]>
> >
> > The Intel Timed IO PPS generator driver outputs a PPS signal using
> > dedicated hardware that is more accurate than software actuated PPS.
> > The Timed IO hardware generates output events using the ART timer.
> > The ART timer period varies based on platform type, but is less than
> > 100 nanoseconds for all current platforms. Timed IO output accuracy is
> > within 1 ART period.
> >
> > PPS output is enabled by writing '1' the 'enable' sysfs attribute. The
> > driver uses hrtimers to schedule a wake-up 10 ms before each event
> > (edge) target time. At wakeup, the driver converts the target time in
> > terms of CLOCK_REALTIME to ART trigger time and writes this to the
> > Timed IO hardware. The Timed IO hardware generates an event precisely
> > at the requested system time without software involvement.
>
> ...
>
> > +static enum hrtimer_restart hrtimer_callback(struct hrtimer *timer) {
> > + struct pps_tio *tio = container_of(timer, struct pps_tio, timer);
> > + ktime_t expires, now;
> > + u32 event_count;
> > +
> > + guard(spinlock)(&tio->lock);
> > +
> > + /* Check if any event is missed. If an event is missed, TIO will be
> disabled*/
> > + event_count = pps_tio_read(tio, TIOEC);
> > + if (tio->prev_count && tio->prev_count == event_count)
> > + goto err;
> > + tio->prev_count = event_count;
> > + expires = hrtimer_get_expires(timer);
> > + now = ktime_get_real();
>
> > + if (now - expires < SAFE_TIME_NS) {
> > + if (!pps_generate_next_pulse(tio, expires +
> SAFE_TIME_NS))
> > + return HRTIMER_NORESTART;
> > + } else {
>
> Redundant.
>
> > + goto err;
> > + }
>
> if (now - expires >= SAFE_TIME_NS)
> goto err;
>
> if (!pps_generate_next_pulse(tio, expires + SAFE_TIME_NS))
> return HRTIMER_NORESTART;
>
>
> > + hrtimer_forward(timer, now, NSEC_PER_SEC / 2);
> > + return HRTIMER_RESTART;
> > +err:
> > + dev_err(tio->dev, "Event missed, Disabling Timed I/O");
> > + pps_tio_disable(tio);
> > + return HRTIMER_NORESTART;
> > +}
>
> --
> With Best Regards,
> Andy Shevchenko
>
Thanks Andy,
Will update as suggested.
Regards,
Sowjanya
