Re: [PATCH v2 2/2] rtc: pcf2127: Run a OTP refresh if not done before

[Philipp Rosenberger]

On 14.01.21 12:11, Alexandre Belloni wrote:
> On 14/01/2021 11:30:37+0100, Philipp Rosenberger wrote:
> > > > +	ret = regmap_set_bits(pcf2127->regmap, PCF2127_REG_CLKOUT,
> > > > +			      PCF2127_BIT_CLKOUT_OTPR);
> > > > +	if (ret < 0) {
> > > > +		dev_err(dev, "%s: OTP refresh (clkout_ctrl) failed.\n", __func__);
> > >
> > > Please drop this error message.
> >
> > If I return from the probe with an error, shouldn't there be an error
> > message? Or should I ignore the problem at all and don't return from the
> > probe?
>
> You can return from probe without an error message.
>
> > > > +		return ret;
> > > > +	}
> > > > +	msleep(100);
> > >
> > > Maybe this should be done just before setting the time. Or if you want
> > > to keep it in probe, then you could optimise by not waiting but ensuring
> > > the time between pcf2127_probe and the first pcf2127_rtc_set_time is
> > > more than 100ms.
> >
> > Doing it just before setting the time might be not the best way. The
> > watchdog might be used before the OTPR is done.
> >
> >  From the PCF2129 manual:
> > | The OTP refresh (see Section 8.3.2 on page 13) should ideally be
> > | executed as the first instruction after start-up and also after a
> > | reset due to an oscillator stop.
> >
> > As I see it this should be done before setting up the watchdog as well. So
> > sleeping if the OTPR wasn't done before might be the most viable solution.
> > So I would check the OTPR and only if the OTPR is not set starting an OTPR
> > and then sleep 100ms.
>
> Indeed, the remaining question is whether you should test OTPR or OSF.
> OSF states: "oscillator has stopped and chip reset has occurred since
> flag was last cleared" if OTPR is always 0 when OSF is 1, then OTPR is
> probably enough.

The datasheet is unclear about that. And I thought about that as well. 
The OSF flag is and should only reset when the time is set. But if I 
reboot or reload the driver without setting the time the OTRP would be 
rerun. So I thought it would be best to only rely on the OTPR bit. If 
someone has a better idea I'm open far that.

Best Regards,
Philipp