Re: [PATCH] disable clkout for rv3028 by default

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

On 04/05/2023 10:32:17+0200, Johannes Kirchmair wrote:
> The rv3028 chip is kind of strange.
> The chip has two inputs one for the buffer battery
> (V_backup) and one for the main power supply (V_dd).
> By default a clk out of the chip is enabled, drawing a big amount of
> current, draining the buffer battery of our board in 3 days.
> There is a mode that would shut down the clk out if powered from
> V_backup, but that would have to be configured as well. In our
> application the battery is connected via V_dd. So disabling the clk by
> default is the way to go for us.
> 

You can't do that, this introduces a glitch in the clock output and will
break existing users. The clock should be disabled automatically by the
CCF when there are no users. Is your kernel built without
CONFIG_COMMON_CLK?

> Signed-off-by: Johannes Kirchmair <johannes.kirchmair@sigmatek.at>
> ---
>  drivers/rtc/rtc-rv3028.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-rv3028.c b/drivers/rtc/rtc-rv3028.c
> index 12c807306893..9e2aaa7a533e 100644
> --- a/drivers/rtc/rtc-rv3028.c
> +++ b/drivers/rtc/rtc-rv3028.c
> @@ -787,7 +787,7 @@ static const struct regmap_config regmap_config = {
>  static int rv3028_probe(struct i2c_client *client)
>  {
>  	struct rv3028_data *rv3028;
> -	int ret, status;
> +	int ret, status, buf;
>  	u32 ohms;
>  	struct nvmem_config nvmem_cfg = {
>  		.name = "rv3028_nvram",
> @@ -826,6 +826,16 @@ static int rv3028_probe(struct i2c_client *client)
>  	if (status & RV3028_STATUS_AF)
>  		dev_warn(&client->dev, "An alarm may have been missed.\n");
>  
> +	ret = regmap_read(rv3028->regmap, RV3028_CLKOUT, &buf);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (buf != RV3028_CLKOUT_FD_MASK) {
> +		ret = rv3028_update_cfg(rv3028, RV3028_CLKOUT, 0xff, RV3028_CLKOUT_FD_MASK); // disable clk out
> +		if (ret < 0)
> +			return ret;
> +	}
> +
>  	rv3028->rtc = devm_rtc_allocate_device(&client->dev);
>  	if (IS_ERR(rv3028->rtc))
>  		return PTR_ERR(rv3028->rtc);
> -- 
> 2.25.1
> 

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