linux-kernel - Re: [PATCH v2 5/5] rtc: pcf85063: set xtal load capacitance from DT

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Message-ID: <20190116211147.GF2627@piout.net>
Date:   Wed, 16 Jan 2019 22:11:47 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Andrew Jeffery <andrew@...id.au>,
        Fabio Estevam <fabio.estevam@....com>,
        Joel Stanley <joel@....id.au>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Urs Fässler <urs.fassler@....ch>,
        Shawn Guo <shawnguo@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-rtc@...r.kernel.org
Subject: Re: [PATCH v2 5/5] rtc: pcf85063: set xtal load capacitance from DT

On 08/01/2019 19:54:14+0100, Sam Ravnborg wrote:
> Add support for specifying the xtal load capacitance in the DT node.
> The pcf85063 supports xtal load capacitance of 7pF or 12.5pF.
> If the rtc has the wrong configuration the time will
> drift several hours/week.
> 
> The driver use the default value 7pF.
> 
> The DT may specify either 7000fF or 12500fF.
> (The DT uses femto Farad to avoid decimal numbers).
> Other values are warned and the driver uses the default value.
> 
> Signed-off-by: Sam Ravnborg <sam@...nborg.org>
> Cc: Alessandro Zummo <a.zummo@...ertech.it>
> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Cc: Urs Fässler <urs.fassler@....ch>
> ---
>  drivers/rtc/rtc-pcf85063.c | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/drivers/rtc/rtc-pcf85063.c b/drivers/rtc/rtc-pcf85063.c
> index 283c2335b01b..0c0b6030627e 100644
> --- a/drivers/rtc/rtc-pcf85063.c
> +++ b/drivers/rtc/rtc-pcf85063.c
> @@ -27,6 +27,7 @@
>  */
>  
>  #define PCF85063_REG_CTRL1		0x00 /* status */
> +#define PCF85063_REG_CTRL1_CAP_SEL	BIT(0)
>  #define PCF85063_REG_CTRL1_STOP		BIT(5)
>  #define PCF85063_REG_CTRL2		0x01
>  
> @@ -180,6 +181,39 @@ static const struct rtc_class_ops pcf85063_rtc_ops = {
>  	.set_time	= pcf85063_rtc_set_time
>  };
>  
> +static int pcf85063_load_capacitance(struct i2c_client *client)
> +{
> +	u32 load;
> +	int rc;
> +	u8 reg;
> +
> +	rc = i2c_smbus_read_byte_data(client, PCF85063_REG_CTRL1);
> +	if (rc < 0)
> +		return rc;
> +
> +	reg = rc;
> +	load = 7000;
> +	of_property_read_u32(client->dev.of_node, "quartz-load-femtofarads",
> +			     &load);
> +
> +	switch (load) {
> +	default:
> +		dev_warn(&client->dev, "Unknown quartz-load-femtofarads value: %d. Assuming 7000",
> +			load);

Alignment is not correct

> +		/* fall through */
> +	case 7000:
> +		reg &= ~PCF85063_REG_CTRL1_CAP_SEL;
> +		break;
> +	case 12500:
> +		reg |= PCF85063_REG_CTRL1_CAP_SEL;
> +		break;
> +	}
> +
> +	rc = i2c_smbus_write_byte_data(client, PCF85063_REG_CTRL1, reg);
> +
> +	return rc;
> +}
> +
>  static int pcf85063_probe(struct i2c_client *client,
>  				const struct i2c_device_id *id)
>  {
> @@ -197,6 +231,11 @@ static int pcf85063_probe(struct i2c_client *client,
>  		return err;
>  	}
>  
> +	err = pcf85063_load_capacitance(client);
> +	if (err < 0)
> +		dev_warn(&client->dev, "failed to set xtal load capacitance: %d",
> +		         err);

This should be using more tabs.

As you can see, I don't have much to add and I'm quite pleased with the
series.

As Rob pointed out, quartz-load-femtofarads should be added in rtc.txt

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