linux-kernel - Re: [PATCH v3 09/14] rtc: pcf2127: set PWRMNG value for PCF2131

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Date:   Fri, 20 Jan 2023 17:39:17 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Bruno Thomsen <bruno.thomsen@...il.com>
Cc:     Hugo Villeneuve <hugo@...ovil.com>, a.zummo@...ertech.it,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Hugo Villeneuve <hvilleneuve@...onoff.com>
Subject: Re: [PATCH v3 09/14] rtc: pcf2127: set PWRMNG value for PCF2131

Hello,

On 07/01/2023 19:36:06+0100, Bruno Thomsen wrote:
> Den tor. 15. dec. 2022 kl. 16.19 skrev Hugo Villeneuve <hugo@...ovil.com>:
> >
> > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> >
> > Default PWRMNG[2:0] bits are set to 000b for PCF2127/29, but to
> > 111b for PCF2131.
> >
> > Set these bits to 000b to select same mode as PCF2127/29.
> >
> > Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> 
> Reviewed-by: Bruno Thomsen <bruno.thomsen@...il.com>
> 
> I think it's a good idea[1] but there have been concerns about
> setting default values in the past[2]. In case somebody needs
> a different behaviour they should add a device tree property.
> 
> [1] https://lore.kernel.org/linux-rtc/20190910143945.9364-1-bruno.thomsen@gmail.com/
> [2] https://lore.kernel.org/linux-rtc/20191211163354.GC1463890@piout.net/

I confirm this is still my point of view and I won't take this patch as
this may break existing users.

> 
> > ---
> >  drivers/rtc/rtc-pcf2127.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> > diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
> > index 68af4d0438b8..241189ee4a05 100644
> > --- a/drivers/rtc/rtc-pcf2127.c
> > +++ b/drivers/rtc/rtc-pcf2127.c
> > @@ -53,6 +53,7 @@
> >  #define PCF2127_BIT_CTRL3_BLF                  BIT(2)
> >  #define PCF2127_BIT_CTRL3_BF                   BIT(3)
> >  #define PCF2127_BIT_CTRL3_BTSE                 BIT(4)
> > +#define PCF2127_CTRL3_PWRMNG_MASK              GENMASK(7, 5)
> >  /* Control register 4 */
> >  #define PCF2131_REG_CTRL4              0x03
> >  #define PCF2131_BIT_CTRL4_TSF4                 BIT(4)
> > @@ -1129,6 +1130,20 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
> >         regmap_clear_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
> >                                 PCF2127_BIT_CTRL1_POR_OVRD);
> >
> > +       /* Make sure PWRMNG[2:0] is set to 000b. This is the default for
> > +        * PCF2127/29, but not for PCF2131 (default of 111b).
> > +        *
> > +        * PWRMNG[2:0]  = 000b:
> > +        *   battery switch-over function is enabled in standard mode;
> > +        *   battery low detection function is enabled
> > +        */
> > +       ret = regmap_clear_bits(pcf2127->regmap, PCF2127_REG_CTRL3,
> > +                               PCF2127_CTRL3_PWRMNG_MASK);
> > +       if (ret < 0) {
> > +               dev_err(dev, "PWRMNG config failed\n");
> > +               return ret;
> > +       }
> > +
> >         ret = regmap_read(pcf2127->regmap, pcf2127->cfg->reg_clkout, &val);
> >         if (ret < 0)
> >                 return ret;
> > --
> > 2.30.2
> >

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