linux-kernel - Re: [PATCH] rtc: pcf2127: align power management configuration

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Message-ID: <CA+gFNtY0q2kyj2kjDbUSdrhkZkcjnwHCau=0Om-akpm-imkYFw@mail.gmail.com>
Date: Tue, 27 May 2025 10:22:23 +0200
From: Giampiero Baggiani <giampiero@...ralabs.cc>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: pcf2127: align power management configuration

Thank you for the prompt feedback Alexandre.

On Mon, May 26, 2025 at 9:39 PM Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
>
> On 26/05/2025 18:12:34+0200, Giampiero Baggiani wrote:
> > The PCF2131 comes with the following default settings:
> > - battery switch-over function is disabled;
> > - battery low detection function is disabled.
> > These defaults differ from those of other models supported by this driver.
> >
> > This commit aligns the behavior across all supported models, configuring
> > them to the settings typically expected from an RTC.
>
> We can't do that as this is going to break existing users as they may rely on
> the current behaviour and the configuration is persistent across reboots.

Would it be ok to use a "backup-switchover-mode" device property?
I guess a "battery-low-detection" property will be needed too, which
would also fix the current issue of BLD config lost when switching
between BSMs.
Thank you.

>
> >
> > Signed-off-by: Giampiero Baggiani <giampiero@...ralabs.cc>
> > ---
> >  drivers/rtc/rtc-pcf2127.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
> > index 31c7dca8f469..cbdf7f23e6a6 100644
> > --- a/drivers/rtc/rtc-pcf2127.c
> > +++ b/drivers/rtc/rtc-pcf2127.c
> > @@ -1312,8 +1312,15 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
> >        * Clear battery interrupt flags which can block new trigger events.
> >        * Note: This is the default chip behaviour but added to ensure
> >        * correct tamper timestamp and interrupt function.
> > +      *
> > +      * Power management functions set to:
> > +      * - battery switch-over function is enabled in standard mode;
> > +      * - battery low detection function is enabled;
> > +      * - extra power fail detection function is enabled.
> > +      * Note: This is the default configuration except for pcf2131.
> >        */
> >       ret = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL3,
> > +                              PCF2127_CTRL3_PM |
> >                                PCF2127_BIT_CTRL3_BTSE |
> >                                PCF2127_BIT_CTRL3_BIE |
> >                                PCF2127_BIT_CTRL3_BLIE, 0);
> > --
> > 2.39.2 (Apple Git-143)
> >
>
> --
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

--
Giampiero Baggiani
Sfera Labs - www.sferalabs.cc