linux-kernel - RE: [PATCH v7 10/12] pps: generators: Add PPS Generator TIO Driver

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Date: Thu, 9 May 2024 04:38:49 +0000
From: "D, Lakshmi Sowjanya" <lakshmi.sowjanya.d@...el.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "jstultz@...gle.com"
	<jstultz@...gle.com>, "giometti@...eenne.com" <giometti@...eenne.com>,
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 Eddie" <eddie.dong@...el.com>, "Hall, Christopher S"
	<christopher.s.hall@...el.com>, "Brandeburg, Jesse"
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 L" <anthony.l.nguyen@...el.com>, "peter.hilber@...nsynergy.com"
	<peter.hilber@...nsynergy.com>, "N, Pandith" <pandith.n@...el.com>, "Mohan,
 Subramanian" <subramanian.mohan@...el.com>, "T R, Thejesh Reddy"
	<thejesh.reddy.t.r@...el.com>
Subject: RE: [PATCH v7 10/12] pps: generators: Add PPS Generator TIO Driver



> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Sent: Tuesday, April 30, 2024 7:23 PM
> To: D, Lakshmi Sowjanya <lakshmi.sowjanya.d@...el.com>
> Cc: tglx@...utronix.de; jstultz@...gle.com; giometti@...eenne.com;
> corbet@....net; linux-kernel@...r.kernel.org; x86@...nel.org;
> netdev@...r.kernel.org; linux-doc@...r.kernel.org; intel-wired-
> lan@...ts.osuosl.org; Dong, Eddie <eddie.dong@...el.com>; Hall, Christopher
> S <christopher.s.hall@...el.com>; Brandeburg, Jesse
> <jesse.brandeburg@...el.com>; davem@...emloft.net;
> alexandre.torgue@...s.st.com; joabreu@...opsys.com;
> mcoquelin.stm32@...il.com; perex@...ex.cz; linux-
> sound@...r.kernel.org; Nguyen, Anthony L <anthony.l.nguyen@...el.com>;
> peter.hilber@...nsynergy.com; N, Pandith <pandith.n@...el.com>; Mohan,
> Subramanian <subramanian.mohan@...el.com>; T R, Thejesh Reddy
> <thejesh.reddy.t.r@...el.com>
> Subject: Re: [PATCH v7 10/12] pps: generators: Add PPS Generator TIO Driver
> 
> On Tue, Apr 30, 2024 at 02:22:23PM +0530, lakshmi.sowjanya.d@...el.com
> wrote:
> > From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
> >
> > 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