> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Sent: Monday, May 13, 2024 4:49 PM
> To: D, Lakshmi Sowjanya <lakshmi.sowjanya.d@xxxxxxxxx>
> Cc: tglx@xxxxxxxxxxxxx; jstultz@xxxxxxxxxx; giometti@xxxxxxxxxxxx;
> corbet@xxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; intel-wired-
> lan@xxxxxxxxxxxxxxxx; Dong, Eddie <eddie.dong@xxxxxxxxx>; Hall, Christopher
> S <christopher.s.hall@xxxxxxxxx>; Brandeburg, Jesse
> <jesse.brandeburg@xxxxxxxxx>; davem@xxxxxxxxxxxxx;
> alexandre.torgue@xxxxxxxxxxx; joabreu@xxxxxxxxxxxx;
> mcoquelin.stm32@xxxxxxxxx; perex@xxxxxxxx; linux-
> sound@xxxxxxxxxxxxxxx; Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>;
> peter.hilber@xxxxxxxxxxxxxxx; N, Pandith <pandith.n@xxxxxxxxx>; Mohan,
> Subramanian <subramanian.mohan@xxxxxxxxx>; T R, Thejesh Reddy
> <thejesh.reddy.t.r@xxxxxxxxx>
> Subject: Re: [PATCH v8 10/12] pps: generators: Add PPS Generator TIO Driver
>
> On Mon, May 13, 2024 at 04:08:11PM +0530, lakshmi.sowjanya.d@xxxxxxxxx
> wrote:
> > From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
> >
> > 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 ssize_t enable_store(struct device *dev, struct device_attribute
> *attr, const char *buf,
> > + size_t count)
> > +{
> > + struct pps_tio *tio = dev_get_drvdata(dev);
> > + bool enable;
> > + int err;
>
> (1)
>
> > + err = kstrtobool(buf, &enable);
> > + if (err)
> > + return err;
> > +
> > + guard(spinlock_irqsave)(&tio->lock);
> > + if (enable && !tio->enabled) {
>
> > + if (!timekeeping_clocksource_has_base(CSID_X86_ART)) {
> > + dev_err(tio->dev, "PPS cannot be started as clock is
> not related
> > +to ART");
>
> Why not simply dev_err(dev, ...)?
>
> > + return -EPERM;
> > + }
>
> I'm wondering if we can move this check to (1) above.
> Because currently it's a good question if we are able to stop PPS which was
> run by somebody else without this check done.
Do you mean can someone stop the signal without this check?
Yes, this check is not required to stop. So, I feel it need not be moved to (1).
Please, correct me if my understanding is wrong.
>
> I.o.w. this sounds too weird to me and reading the code doesn't give any hint
> if it's even possible. And if it is, are we supposed to touch that since it was
> definitely *not* us who ran it.
Yes, we are not restricting on who can stop/start the signal.
>
> > + pps_tio_direction_output(tio);
> > + hrtimer_start(&tio->timer, first_event(tio),
> HRTIMER_MODE_ABS);
> > + tio->enabled = true;
> > + } else if (!enable && tio->enabled) {
> > + hrtimer_cancel(&tio->timer);
> > + pps_tio_disable(tio);
> > + tio->enabled = false;
> > + }
> > + return count;
> > +}
>
> ...
>
> > +static int pps_tio_probe(struct platform_device *pdev) {
>
> struct device *dev = &pdev->dev;
>
> > + struct pps_tio *tio;
> > +
> > + if (!(cpu_feature_enabled(X86_FEATURE_TSC_KNOWN_FREQ) &&
> > + cpu_feature_enabled(X86_FEATURE_ART))) {
> > + dev_warn(&pdev->dev, "TSC/ART is not enabled");
>
> dev_warn(dev, "TSC/ART is not enabled");
>
> > + return -ENODEV;
> > + }
> > +
> > + tio = devm_kzalloc(&pdev->dev, sizeof(*tio), GFP_KERNEL);
>
> tio = devm_kzalloc(dev, sizeof(*tio), GFP_KERNEL);
>
>
> > + if (!tio)
> > + return -ENOMEM;
> > +
> > + tio->dev = &pdev->dev;
>
> tio->dev = dev;
>
> > + tio->base = devm_platform_ioremap_resource(pdev, 0);
> > + if (IS_ERR(tio->base))
> > + return PTR_ERR(tio->base);
>
> > + pps_tio_disable(tio);
>
> This...
>
> > + hrtimer_init(&tio->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
> > + tio->timer.function = hrtimer_callback;
> > + spin_lock_init(&tio->lock);
>
> > + tio->enabled = false;
>
> ...and this should go together, which makes me look at the enabled flag over
> the code and it seems there are a few places where you missed to sync it
> with the reality.
>
> I would think of something like this:
>
> pps_tio_direction_output() ==> true
> pps_tio_disable(tio) ==> false
>
> where "==> X" means assignment of enabled flag.
>
> And perhaps this:
>
> tio->enabled = pps_generate_next_pulse(tio, expires +
> SAFE_TIME_NS);
> if (!tio->enabled)
> ...
>
> But the above is just thinking out loudly, you may find the better
> approach(es).
Yeah, makes sense.
Will add enable counterpart.
Will update tio->enabled in disable and enable functions.
>
> > + platform_set_drvdata(pdev, tio);
> > +
> > + return 0;
> > +}
>
> --
> With Best Regards,
> Andy Shevchenko
>
Regards,
Lakshmi Sowjanya
