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

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Date: Tue, 30 Apr 2024 16:53:18 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: 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, eddie.dong@...el.com,
	christopher.s.hall@...el.com, 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, anthony.l.nguyen@...el.com,
	peter.hilber@...nsynergy.com, pandith.n@...el.com,
	subramanian.mohan@...el.com, 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