linux-kernel - RE: [PATCH 1/2] dt-bindings: hwmon: max31827: use supply pin name

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Date:   Sat, 23 Sep 2023 14:19:45 +0000
From:   "Miclaus, Antoniu" <Antoniu.Miclaus@...log.com>
To:     Rob Herring <robh@...nel.org>
CC:     "Matyas, Daniel" <Daniel.Matyas@...log.com>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] dt-bindings: hwmon: max31827: use supply pin name



> On Thu, Sep 21, 2023 at 05:20:03PM +0300, Antoniu Miclaus wrote:
> > The actual hardware pin name for the supply of max31827 is vdd.
> > Update the dt-binding to reflect the hardware properties accordingly.
> 
> Changing this breaks the ABI. I see the old one wasn't used by the
> driver, but that's just one driver potentially. You need some
> justification here why it's okay to break the ABI.
> 
As I mentioned also in the commit description, the supply should match the
actual hardware pin name. Otherwise it might create confusion. Usually vref
refers to an external voltage reference pin used for ADC/DACs which is not
exactly the case for this part, taking into account that there is no "reference"
word mentioned in the datasheet at all. VREF and VDD are usually separate
hardware pins. There is a hint indeed in the dts example that the vref-supply 
might be referenced to a vdd regulator node, but from my point of view
that is not enough. Moreover the current vref-supply is not handled at all in
the driver, it is only mentioned in the dt-binding (That's why I added a second
patch in the series handling the supply).

If the justification is not enough to apply this change, then I can keep only the
second patch, which handles the regulator in the driver and use the  old `vref`
naming which currently appears only in the dt-binding.

Antoniu
> >
> > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
> > ---
> >  Documentation/devicetree/bindings/hwmon/adi,max31827.yaml | 6 +++--
> -
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git
> a/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
> b/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
> > index 2dc8b07b4d3b..21f2d350373b 100644
> > --- a/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
> > +++ b/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
> > @@ -27,7 +27,7 @@ properties:
> >    reg:
> >      maxItems: 1
> >
> > -  vref-supply:
> > +  vdd-supply:
> >      description:
> >        Must have values in the interval (1.6V; 3.6V) in order for the device to
> >        function correctly.
> > @@ -35,7 +35,7 @@ properties:
> >  required:
> >    - compatible
> >    - reg
> > -  - vref-supply
> > +  - vdd-supply
> >
> >  additionalProperties: false
> >
> > @@ -48,7 +48,7 @@ examples:
> >          temperature-sensor@42 {
> >              compatible = "adi,max31827";
> >              reg = <0x42>;
> > -            vref-supply = <&reg_vdd>;
> > +            vdd-supply = <&reg_vdd>;
> >          };
> >      };
> >  ...
> > --
> > 2.42.0
> >