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

[Philipp Rosenberger]

On 14.01.21 10:50, Alexandre Belloni wrote:
> On 13/01/2021 12:27:42+0100, Philipp Rosenberger wrote:
> > The datasheet of the PCF2127 states,it is recommended to process an OTP
> > refresh once the power is up and the oscillator is operating stable. The
> > OTP refresh takes less than 100 ms to complete.
> >
> > Signed-off-by: Philipp Rosenberger <p.rosenberger@xxxxxxxxxx>
> > ---
> >   drivers/rtc/rtc-pcf2127.c | 16 ++++++++++++++++
> >   1 file changed, 16 insertions(+)
> >
> > diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
> > index 378b1ce812d6..ca56dba64e79 100644
> > --- a/drivers/rtc/rtc-pcf2127.c
> > +++ b/drivers/rtc/rtc-pcf2127.c
> > @@ -58,6 +58,9 @@
> >   #define PCF2127_REG_ALARM_DM		0x0D
> >   #define PCF2127_REG_ALARM_DW		0x0E
> >   #define PCF2127_BIT_ALARM_AE			BIT(7)
> > +/* CLKOUT control register */
> > +#define PCF2127_REG_CLKOUT		0x0f
> > +#define PCF2127_BIT_CLKOUT_OTPR			BIT(5)
> >   /* Watchdog registers */
> >   #define PCF2127_REG_WD_CTL		0x10
> >   #define PCF2127_BIT_WD_CTL_TF0			BIT(0)
> > @@ -630,6 +633,19 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
> >   		dev_warn(dev, "Watchdog and alarm functions might not work properly\n");
> >   	}
> >   
> > +	/*
> > +	 * Set the OTP refresh bit unconditionally. If an OTP refresh was
> > +	 * already done the bit is already set and will not rerun the refresh
> > +	 * operation.
> > +	 */
> > +	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?

> > +		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.

Best Regards
Philipp