linux-kernel - Re: [PATCH 2/2] rtc: pcf85063: handle stopped oscillator at startup

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Message-ID: <202504100917398f7244e9@mail.local>
Date: Thu, 10 Apr 2025 11:17:39 +0200
From: Alexandre Belloni <alexandre.belloni@...tlin.com>
To: Ciprian Costea <ciprianmarian.costea@....nxp.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Alexander Stein <alexander.stein@...tq-group.com>,
	linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, s32@....com, imx@...ts.linux.dev,
	Christophe Lizzi <clizzi@...hat.com>,
	Alberto Ruiz <aruizrui@...hat.com>,
	Enric Balletbo <eballetb@...hat.com>,
	Eric Chanudet <echanude@...hat.com>,
	Larisa Grigore <larisa.grigore@....com>
Subject: Re: [PATCH 2/2] rtc: pcf85063: handle stopped oscillator at startup

On 10/04/2025 11:25:48+0300, Ciprian Costea wrote:
> From: Ciprian Marian Costea <ciprianmarian.costea@....nxp.com>
> 
> If the RTC is not linked to any battery, the oscillator is stopped at
> startup and a SW reset command is generated to the PCF85063 RTC.
> Manually start the oscillator in case the PCF85063 RTC is not battery
> backed.
> 

No, there is no point in starting the oscillator with a know wrong
time/date. The oscillator must only be started once the time is known
good, that is in .set_time

> Co-developed-by: Larisa Grigore <larisa.grigore@....com>
> Signed-off-by: Larisa Grigore <larisa.grigore@....com>
> Signed-off-by: Ciprian Marian Costea <ciprianmarian.costea@....nxp.com>
> ---
>  drivers/rtc/rtc-pcf85063.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/rtc/rtc-pcf85063.c b/drivers/rtc/rtc-pcf85063.c
> index 4fa5c4ecdd5a..6de7344d2469 100644
> --- a/drivers/rtc/rtc-pcf85063.c
> +++ b/drivers/rtc/rtc-pcf85063.c
> @@ -590,6 +590,14 @@ static int pcf85063_probe(struct i2c_client *client)
>  
>  	i2c_set_clientdata(client, pcf85063);
>  
> +	if (of_property_read_bool(client->dev.of_node, "no-battery")) {
> +		err = regmap_update_bits(pcf85063->regmap, PCF85063_REG_SC,
> +					 PCF85063_REG_SC_OS, 0);
> +		if (err)
> +			return dev_err_probe(&client->dev, err,
> +					"Failed to start the oscillator\n");
> +	}
> +
>  	err = regmap_read(pcf85063->regmap, PCF85063_REG_SC, &tmp);
>  	if (err)
>  		return dev_err_probe(&client->dev, err, "RTC chip is not present\n");
> -- 
> 2.45.2
> 

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