linux-kernel - Re: [PATCH v2 1/2] dt-bindings: rtc: pcf2127: Add nxp,battery-switch-over property

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Message-ID: <sopwritiludrmxzupp3p62ngak3u7qekyam67qh23qnchjim4w@eft6y6kuuqbj>
Date: Wed, 23 Oct 2024 09:06:59 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Conor Dooley <conor@...nel.org>
Cc: Philipp Rosenberger <p.rosenberger@...bus.com>, 
	Alexandre Belloni <alexandre.belloni@...tlin.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, linux-rtc@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH v2 1/2] dt-bindings: rtc: pcf2127: Add
 nxp,battery-switch-over property

On Tue, Oct 22, 2024 at 05:35:55PM +0100, Conor Dooley wrote:
> On Tue, Oct 22, 2024 at 11:28:54AM +0200, Philipp Rosenberger wrote:
> > The nxp,battery-switch-over property is used to control the switch-over,
> > battery low detection and extra power fail detection functions.
> > 
> > The PCF2131 has a different default value for the PWRMNG bits. It is set
> > to 0x7: battery switch-over function is disabled, only one power supply
> > (VDD); battery low detection function is disabled.
> > This is the opposite of the default of the PCF2127/PCA2129 and PCF2129.
> > With the nxp,battery-switch-over the behavior can be controlled through
> > the device tree.
> > 
> > Signed-off-by: Philipp Rosenberger <p.rosenberger@...bus.com>
> > ---
> >  Documentation/devicetree/bindings/rtc/nxp,pcf2127.yaml | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/rtc/nxp,pcf2127.yaml b/Documentation/devicetree/bindings/rtc/nxp,pcf2127.yaml
> > index 2d9fe5a75b06..5739c3e371e7 100644
> > --- a/Documentation/devicetree/bindings/rtc/nxp,pcf2127.yaml
> > +++ b/Documentation/devicetree/bindings/rtc/nxp,pcf2127.yaml
> > @@ -30,6 +30,16 @@ properties:
> >  
> >    reset-source: true
> >  
> > +  nxp,battery-switch-over:
> > +    description:
> > +      Battery and power related configuration. This property is used to set the
> > +      PWRMNG bits of the Control_3 register to control the battery switch-over,
> > +      battery low detection and extra power fail detection functions.
> > +      The actual supported functions depend on the device capabilities.
> > +    $ref: /schemas/types.yaml#/definitions/uint8
> > +    minimum: 0
> > +    maximum: 7
> 
> Beyond the fact that I dislike register-content properties like this, where
> it is not possible to grok the meaning by reading the property, what
> even makes this suitable for DT in the first place? Reading the commit
> message this sounds like software policy, and that different users of
> the same board might want to configure these register bits in different
> ways.

Especially that according to commit msg this is model specific, so
compatible already defines different default value of this register.

Best regards,
Krzysztof