Re: [PATCH v2 1/3] dt-bindings: rtc: pcf8523: add DSM pm option for battery switch-over

From: Alexandre Belloni <alexandre.belloni@bootlin•com>
To: Rob Herring <robh@kernel•org>
Cc: a.zummo@towertech•it, baruch@tkos•co.il, kernel@pengutronix•de,
	devicetree@vger•kernel.org, festevam@gmail•com,
	s.hauer@pengutronix•de, linux@armlinux•org.uk,
	linux-kernel@vger•kernel.org, linux-imx@nxp•com,
	miguelborgesdefreitas@gmail•com, shawnguo@kernel•org,
	linux-arm-kernel@lists•infradead.org
Subject: Re: [PATCH v2 1/3] dt-bindings: rtc: pcf8523: add DSM pm option for battery switch-over
Date: Thu, 23 Jul 2020 21:57:55 +0200	[thread overview]
Message-ID: <20200723195755.GV3428@piout.net> (raw)
In-Reply-To: <20200723174905.GA596242@bogus>

On 23/07/2020 11:49:05-0600, Rob Herring wrote:
> On Mon, Jul 20, 2020 at 12:23:59PM +0100, miguelborgesdefreitas@gmail•com wrote:
> > From: Miguel Borges de Freitas <miguelborgesdefreitas@gmail•com>
> > 
> > This adds direct-switching mode as a configurable DT flag for
> > RTC modules supporting it (e.g. nxp pcf8523).
> > DSM switches the power source to the battery supply whenever the
> > VDD drops below VBAT. The option is recommended for hw designs
> > where VDD is always expected to be higher than VBAT.
> > 
> > Signed-off-by: Miguel Borges de Freitas <miguelborgesdefreitas@gmail•com>
> > ---
> > Changes in v2:
> > - Added extended commit message for git history
> > - Separate dt bindings documentation into a single patch
> > 
> >  Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt | 7 ++++++-
> >  Documentation/devicetree/bindings/rtc/rtc.yaml        | 7 +++++++
> >  2 files changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
> > index 0b1080c..f715a8f 100644
> > --- a/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
> > +++ b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
> > @@ -4,10 +4,14 @@ Required properties:
> >  - compatible: Should contain "nxp,pcf8523".
> >  - reg: I2C address for chip.
> >  
> > -Optional property:
> > +Optional properties:
> >  - quartz-load-femtofarads: The capacitive load of the quartz(x-tal),
> >    expressed in femto Farad (fF). Valid values are 7000 and 12500.
> >    Default value (if no value is specified) is 12500fF.
> > +- pm-enable-dsm: battery switch-over function is enabled in direct
> > +  switching mode. The power failure condition happens when VDD < VBAT,
> > +  without requiring VDD to drop below Vth(sw)bat.
> > +  Default value (if not provided) is the standard mode.
> >  
> >  Example:
> >  
> > @@ -15,4 +19,5 @@ pcf8523: rtc@68 {
> >  	compatible = "nxp,pcf8523";
> >  	reg = <0x68>;
> >  	quartz-load-femtofarads = <7000>;
> > +	pm-enable-dsm;
> >  };
> > diff --git a/Documentation/devicetree/bindings/rtc/rtc.yaml b/Documentation/devicetree/bindings/rtc/rtc.yaml
> > index ee237b2..a0048f4 100644
> > --- a/Documentation/devicetree/bindings/rtc/rtc.yaml
> > +++ b/Documentation/devicetree/bindings/rtc/rtc.yaml
> > @@ -47,4 +47,11 @@ properties:
> >      description:
> >        Enables wake up of host system on alarm.
> >  
> > +  pm-enable-dsm:
> > +    $ref: /schemas/types.yaml#/definitions/flag
> > +    description:
> > +      Enables the battery switch-over function in direct switching
> > +      mode. Should be set in systems where VDD is higher than VBAT
> > +      at all times.
> 
> I'm all for common properties, but is this common across vendors?
> 

This is but this shouldn't be a DT property as it has to be changed
dynamically. I'm working on an ioctl interface to change this
configuration.

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

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