linux-kernel - Re: [PATCH] rtc: pcf85063: Add support for specifying the clkout frequency from device tree node.

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Date:   Fri, 19 Jul 2019 15:56:30 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Michael McCormick <michael.mccormick@...tel.net>
Cc:     a.zummo@...ertech.it, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: pcf85063: Add support for specifying the clkout
 frequency from device tree node.

Hello,

On 04/07/2019 14:24:39+1200, Michael McCormick wrote:
> Primarily this allows the clkout signal to be disabled and save some
> power when running off battery backup. However, all hardware implemented
> values are implemented. Uses default value of 32768Hz if node is not
> specified.
> 

the proper way of doing that is to register the clkout signal in the
common clock framework. You can hava a look at rtc-pcf8563.c or rtc-m41t80.c

> Signed-off-by: Michael McCormick <michael.mccormick@...tel.net>
> ---
>  drivers/rtc/rtc-pcf85063.c | 52 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 52 insertions(+)
> 
> diff --git a/drivers/rtc/rtc-pcf85063.c b/drivers/rtc/rtc-pcf85063.c
> index 1afa6d9fa9fb..5c19381899ed 100644
> --- a/drivers/rtc/rtc-pcf85063.c
> +++ b/drivers/rtc/rtc-pcf85063.c
> @@ -37,6 +37,9 @@
>  #define PCF85063_REG_CTRL2             0x01
>  #define PCF85063_CTRL2_AF              BIT(6)
>  #define PCF85063_CTRL2_AIE             BIT(7)
> +#define PCF85063_CTRL2_COF2            BIT(2)
> +#define PCF85063_CTRL2_COF1            BIT(1)
> +#define PCF85063_CTRL2_COF0            BIT(0)
> 
>  #define PCF85063_REG_OFFSET            0x02
>  #define PCF85063_OFFSET_SIGN_BIT       6       /* 2's complement sign bit */
> @@ -369,6 +372,51 @@ static int pcf85063_load_capacitance(struct pcf85063 *pcf85063,
>                                   PCF85063_REG_CTRL1_CAP_SEL, reg);
>  }
> 
> +static int pcf85063_set_clkout_mode(struct pcf85063 *pcf85063,
> +                                   const struct device_node *np)
> +{
> +       u32 load = 32768;
> +       u8 reg = 0;
> +
> +       of_property_read_u32(np, "clockout-frequency", &load);
> +       switch (load) {
> +       case 0:
> +               reg = PCF85063_CTRL2_COF2 | PCF85063_CTRL2_COF1 |
> +                     PCF85063_CTRL2_COF0;
> +               break;
> +       case 1:
> +               reg = PCF85063_CTRL2_COF2 | PCF85063_CTRL2_COF1;
> +               break;
> +       case 1024:
> +               reg = PCF85063_CTRL2_COF2 | PCF85063_CTRL2_COF0;
> +               break;
> +       case 2048:
> +               reg = PCF85063_CTRL2_COF2;
> +               break;
> +       case 4096:
> +               reg = PCF85063_CTRL2_COF1 | PCF85063_CTRL2_COF0;
> +               break;
> +       case 8192:
> +               reg = PCF85063_CTRL2_COF1;
> +               break;
> +       case 16384:
> +               reg = PCF85063_CTRL2_COF0;
> +               break;
> +       case 32768:
> +               reg = 0;
> +               break;
> +       default:
> +               dev_warn(&pcf85063->rtc->dev,
> +                       "Unknown clockout-frequency: %d. Assuming 32768", load);
> +               reg = 0;
> +               break;
> +       }
> +
> +       return regmap_update_bits(pcf85063->regmap, PCF85063_REG_CTRL2,
> +                                 PCF85063_CTRL2_COF2 | PCF85063_CTRL2_COF1 |
> +                                 PCF85063_CTRL2_COF0, reg);
> +}
> +
>  static const struct pcf85063_config pcf85063a_config = {
>         .regmap = {
>                 .reg_bits = 8,
> @@ -443,6 +491,10 @@ static int pcf85063_probe(struct i2c_client *client)
>                 dev_warn(&client->dev, "failed to set xtal load capacitance: %d",
>                          err);
> 
> +       err = pcf85063_set_clkout_mode(pcf85063, client->dev.of_node);
> +       if (err < 0)
> +               dev_warn(&client->dev, "failed to set clock out mode: %d", err);
> +
>         pcf85063->rtc->ops = &pcf85063_rtc_ops;
>         pcf85063->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
>         pcf85063->rtc->range_max = RTC_TIMESTAMP_END_2099;
> --
> 2.17.1
> 
> 
> 
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-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com