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

["Sverdlin, Alexander" <alexander.sverdlin@siemens.com>]

Hi Alexandre,

On Mon, 2026-08-24 at 10:24 +0200, Alexandre Belloni wrote:
> > From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> > 
> > 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.

There is late_initcall_sync(clk_disable_unused) (marked __init), but for the
clock providers registered later, say, via modules, there is no such mechanism.
And I double-checked this putting some debug prints into the driver,
nothing from struct clk_ops is being called without a consumer in DT.

> > 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@siemens.com>
> > ---
> >  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
> > 

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com