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

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Date:   Mon, 25 Sep 2023 08:54:49 +0200
From:   Nuno Sá <noname.nuno@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        "Miclaus, Antoniu" <Antoniu.Miclaus@...log.com>
Cc:     Rob Herring <robh@...nel.org>,
        "Matyas, Daniel" <Daniel.Matyas@...log.com>,
        Jean Delvare <jdelvare@...e.com>,
        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 Sun, 2023-09-24 at 05:02 -0700, Guenter Roeck wrote:
> On Sat, Sep 23, 2023 at 02:19:45PM +0000, Miclaus, Antoniu wrote:
> > 
> > 
> > > 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.
> > 
> 
> That would have been a good argument when the property was introduced, but if
> there are any systems with existing bindings out there they will use the old
> name and fail after this change is applied.
> 

How about introducing the new property and add 'deprecated: true' to the old one. I
guess the second patch would still remain as-is. Or is this just not worth the noise?

- Nuno Sá