Re: [PATCH] rtc: pcf85063: disable the clkout output by default

[Alexandre Belloni]

On 24/08/2026 10:07:59+0200, A. Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
> 
> The PCF85063 powers up with its CLKOUT pin driving the 32.768 kHz. While
> it's possible to request a specific default frequency in the DT via
> assigned-clocks/assigned-clock-rates on the RTC node itself, even without
> a real consumer referencing the clock, there is no such possibility to
> disable the clock output by default.

Are you sure about this? The CCF should disable the clock if it is not
used.

> 
> Therefore gate CLKOUT in the driver before registering the OF provider,
> mirroring the pcf8563 and hym8563 siblings which already force an off state
> at registration. Doing it before devm_of_clk_add_hw_provider() leaves the
> real consumers in the device tree free to re-enable the output afterwards,
> while an otherwise unused CLKOUT now stays off.
> 
> In practice it means that with CLKOUT disabled the RTC consumes around
> 250nA at 25°C and 6-10uA with CLKOUT enabled (5v Vdd). Which means days vs
> hours on a supercapacitor.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
> ---
>  drivers/rtc/rtc-pcf85063.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/rtc/rtc-pcf85063.c b/drivers/rtc/rtc-pcf85063.c
> index 01e209d88f5f3..0b6d8083b6456 100644
> --- a/drivers/rtc/rtc-pcf85063.c
> +++ b/drivers/rtc/rtc-pcf85063.c
> @@ -523,6 +523,12 @@ static struct clk *pcf85063_clkout_register_clk(struct pcf85063 *pcf85063)
>  	/* optional override of the clockname */
>  	of_property_read_string(node, "clock-output-names", &init.name);
>  
> +	/* power-on default is the 32768 Hz output on; gate it until claimed */
> +	ret = regmap_update_bits(pcf85063->regmap, PCF85063_REG_CTRL2,
> +				 PCF85063_REG_CLKO_F_MASK, PCF85063_REG_CLKO_F_OFF);
> +	if (ret)
> +		return ret;
> +
>  	/* register the clock */
>  	clk = devm_clk_register(&pcf85063->rtc->dev, &pcf85063->clkout_hw);
>  
> -- 
> 2.55.0
> 

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