linux-kernel - Re: [PATCH v2 1/3] rtc: tps6594: add driver for TPS6594 PMIC RTC

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Message-ID: <20230328133429ff45c492@mail.local>
Date:   Tue, 28 Mar 2023 15:34:29 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Esteban Blanc <eblanc@...libre.com>
Cc:     linus.walleij@...aro.org, lgirdwood@...il.com, broonie@...nel.org,
        a.zummo@...ertech.it, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-rtc@...r.kernel.org,
        jpanis@...libre.com, jneanne@...libre.com, sterzik@...com,
        u-kumar1@...com
Subject: Re: [PATCH v2 1/3] rtc: tps6594: add driver for TPS6594 PMIC RTC

On 28/03/2023 15:01:05+0200, Esteban Blanc wrote:
> On Tue Mar 28, 2023 at 11:29 AM CEST, Alexandre Belloni wrote:
> > Hello,
> >
> > On 28/03/2023 11:14:46+0200, Esteban Blanc wrote:
> > > +	/* Start rtc */
> > > +	ret = regmap_set_bits(tps->regmap, TPS6594_REG_RTC_CTRL_1,
> > > +			      TPS6594_BIT_STOP_RTC);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +
> > > +	mdelay(100);
> > > +
> > > +	/*
> > > +	 * RTC should be running now. Check if this is the case.
> > > +	 * If not it might be a missing oscillator.
> > > +	 */
> > > +	ret = regmap_test_bits(tps->regmap, TPS6594_REG_RTC_STATUS,
> > > +			       TPS6594_BIT_RUN);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +	if (ret == 0)
> > > +		return -ENODEV;
> > > +
> > > +	/* Stop RTC until first call to `tps6594_rtc_set_time */
> > > +	ret = regmap_clear_bits(tps->regmap, TPS6594_REG_RTC_CTRL_1,
> > > +				TPS6594_BIT_STOP_RTC);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +
> >
> > This whole block must not be executed when the RTC is already running,
> > else, you are stopping a perfectly running RTC.
> 
> I'm not sure to get your point. You mean that during probe, the driver
> might encounter an RTC device that is already running with a correct
> timestamp? How would this be possible? A previous bootstage or the
> driver was removed then re-inserted again?
> 

The whole point of having an RTC is that the time tracking survives a
reboot so yes, I would expect the RTC to have a valid timestamp at probe
time.


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