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

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Message-ID: <20210114080656.ee7fdqufu2biyy4y@pengutronix.de>
Date:   Thu, 14 Jan 2021 09:06:56 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Philipp Rosenberger <p.rosenberger@...bus.com>
Cc:     dan.carpenter@...cle.com, biwen.li@....com, lvb@...hos.com,
        bruno.thomsen@...il.com, l.sanfilippo@...bus.com,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] rtc: pcf2127: Run a OTP refresh if not done before

On Wed, Jan 13, 2021 at 12:27:42PM +0100, Philipp Rosenberger wrote:
> The datasheet of the PCF2127 states,it is recommended to process an OTP

s/,/, /

> 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@...bus.com>
> ---
>  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__);
> +		return ret;
> +	}
> +	msleep(100);

This unconditional sleep isn't so nice. Maybe it makes sense to only do
this when the chip reports a power loss?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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