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SubjectRe: [PATCH v2 4/5] rtc: pcf8523: set xtal load capacitance from DT
On 08/01/2019 19:54:13+0100, Sam Ravnborg wrote:
> Add support for specifying the xtal load capacitance in the DT node.
> The pcf8523 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 12.5pF.
>
> 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@ravnborg.org>
> Cc: Alessandro Zummo <a.zummo@towertech.it>
> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
> ---
> drivers/rtc/rtc-pcf8523.c | 28 ++++++++++++++++++++--------
> 1 file changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/rtc/rtc-pcf8523.c b/drivers/rtc/rtc-pcf8523.c
> index 3fcd2cbafc84..dbbc00b53b50 100644
> --- a/drivers/rtc/rtc-pcf8523.c
> +++ b/drivers/rtc/rtc-pcf8523.c
> @@ -97,8 +97,9 @@ static int pcf8523_voltage_low(struct i2c_client *client)
> return !!(value & REG_CONTROL3_BLF);
> }
>
> -static int pcf8523_select_capacitance(struct i2c_client *client, bool high)
> +static int pcf8523_load_capacitance(struct i2c_client *client)
> {
> + u32 load;
> u8 value;
> int err;
>
> @@ -106,14 +107,24 @@ static int pcf8523_select_capacitance(struct i2c_client *client, bool high)
> if (err < 0)
> return err;
>
> - if (!high)
> - value &= ~REG_CONTROL1_CAP_SEL;
> - else
> + load = 12500;
> + 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 12500",
> + load);

This alignment is not correct, as you will be respinning for the DT doc,
please fix ;)

> + /* fall through */
> + case 12500:
> value |= REG_CONTROL1_CAP_SEL;
> + break;
> + case 7000:
> + value &= ~REG_CONTROL1_CAP_SEL;
> + break;
> + }
>
> err = pcf8523_write(client, REG_CONTROL1, value);
> - if (err < 0)
> - return err;
>
> return err;
> }
> @@ -347,9 +358,10 @@ static int pcf8523_probe(struct i2c_client *client,
> if (!pcf)
> return -ENOMEM;
>
> - err = pcf8523_select_capacitance(client, true);
> + err = pcf8523_load_capacitance(client);
> if (err < 0)
> - return err;
> + dev_warn(&client->dev, "failed to set xtal load capacitance: %d",
> + err);
Ditto

>
> err = pcf8523_set_pm(client, 0);
> if (err < 0)
> --
> 2.12.0
>

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

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