linux-kernel - Re: [PATCH 1/2] rtc: pcf85363: add support for the quartz-load-femtofarads property

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Message-ID: <Y+ptbuZWXrVigvKz@mail.local>
Date:   Mon, 13 Feb 2023 18:03:42 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Javier Carrasco <javier.carrasco@...fvision.net>
Cc:     linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Michael Riesch <michael.riesch@...fvision.net>
Subject: Re: [PATCH 1/2] rtc: pcf85363: add support for the
 quartz-load-femtofarads property

On 13/02/2023 10:50:17+0100, Javier Carrasco wrote:
> The quartz oscillator load capacitance of the PCF85263 and PCF85363 can
> be adjusted to 6 pF, 7 pF (default) and 12.5 pF with the CL[1:0] bits in
> the oscillator control register (address 25h).
> 
> Signed-off-by: Javier Carrasco <javier.carrasco@...fvision.net>
> ---
>  drivers/rtc/rtc-pcf85363.c | 37 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-pcf85363.c b/drivers/rtc/rtc-pcf85363.c
> index c05b722f0060..941f9264cf0a 100644
> --- a/drivers/rtc/rtc-pcf85363.c
> +++ b/drivers/rtc/rtc-pcf85363.c
> @@ -101,6 +101,10 @@
>  #define PIN_IO_INTA_OUT	2
>  #define PIN_IO_INTA_HIZ	3
>  
> +#define OSC_CAP_SEL	GENMASK(1, 0)
> +#define OSC_CAP_6000	0x01
> +#define OSC_CAP_12500	0x02
> +
>  #define STOP_EN_STOP	BIT(0)
>  
>  #define RESET_CPR	0xa4
> @@ -117,6 +121,32 @@ struct pcf85x63_config {
>  	unsigned int num_nvram;
>  };
>  
> +static int pcf85363_load_capacitance(struct pcf85363 *pcf85363, struct device_node *node)
> +{
> +	u32 load = 7000;
> +	u8 value = 0;
> +
> +	of_property_read_u32(node, "quartz-load-femtofarads", &load);
> +
> +	switch (load) {
> +	default:
> +		dev_warn(&pcf85363->rtc->dev, "Unknown quartz-load-femtofarads value: %d. Assuming 7000",
> +			 load);
> +		fallthrough;
> +	case 7000:
> +		break;
> +	case 6000:
> +		value |= OSC_CAP_6000;

Why are you using the |= operator?

> +		break;
> +	case 12500:
> +		value |= OSC_CAP_12500;
> +		break;
> +	}
> +
> +	return regmap_update_bits(pcf85363->regmap, CTRL_OSCILLATOR,
> +				  OSC_CAP_SEL, value);
> +}
> +
>  static int pcf85363_rtc_read_time(struct device *dev, struct rtc_time *tm)
>  {
>  	struct pcf85363 *pcf85363 = dev_get_drvdata(dev);
> @@ -372,7 +402,7 @@ static int pcf85363_probe(struct i2c_client *client)
>  			.reg_write = pcf85363_nvram_write,
>  		},
>  	};
> -	int ret, i;
> +	int ret, i, err;
>  
>  	if (data)
>  		config = data;
> @@ -394,6 +424,11 @@ static int pcf85363_probe(struct i2c_client *client)
>  	if (IS_ERR(pcf85363->rtc))
>  		return PTR_ERR(pcf85363->rtc);
>  
> +	err = pcf85363_load_capacitance(pcf85363, client->dev.of_node);
> +	if (err < 0)
> +		dev_warn(&client->dev, "failed to set xtal load capacitance: %d",
> +			 err);
> +
>  	pcf85363->rtc->ops = &rtc_ops;
>  	pcf85363->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
>  	pcf85363->rtc->range_max = RTC_TIMESTAMP_END_2099;
> -- 
> 2.37.2
> 
> 
> Javier Carrasco 
> Research and Development
> 
> Wolfvision GmbH 
> Oberes Ried 14 | 6833 Klaus | Austria 
> Tel: +43 5523 52250 <tel:+43552352250> | Mail: javier.carrasco@...fvision.net <mailto:javier.carrasco@...fvision.net>
> 
> Website: wolfvision.com <www.wolfvision.com> 
> Firmenbuch / Commercial Register: FN283521v Feldkirch/Austria
> 

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