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Date:   Thu, 14 Jan 2021 12:11:57 +0100
From:   Alexandre Belloni <alexandre.belloni@bootlin.com>
To:     Philipp Rosenberger <p.rosenberger@kunbus.com>
Cc:     dan.carpenter@oracle.com, u.kleine-koenig@pengutronix.de,
        biwen.li@nxp.com, lvb@xiphos.com, bruno.thomsen@gmail.com,
        l.sanfilippo@kunbus.com, Alessandro Zummo <a.zummo@towertech.it>,
        linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] rtc: pcf2127: Run a OTP refresh if not done before
Message-ID: <20210114111157.GC3654@piout.net>
References: <20210113112742.7354-1-p.rosenberger@kunbus.com>
 <20210113112742.7354-3-p.rosenberger@kunbus.com>
 <20210114095008.GV3654@piout.net>
 <77d07f5e-2891-21d6-feee-19e841a8343e@kunbus.com>
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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.


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com