linux-kernel - Re: [PATCH v1 2/8] dt-bindings: iio: dac: maxim,ds4424: add maxim,rfs-ohms property

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Message-ID: <20260123092819.6ae81211@jic23-huawei>
Date: Fri, 23 Jan 2026 09:28:19 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Conor Dooley <conor@...nel.org>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, kernel@...gutronix.de, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org, Andy Shevchenko
 <andy@...nel.org>, David Lechner <dlechner@...libre.com>, Nuno
 Sá <nuno.sa@...log.com>, David Jander <david@...tonic.nl>
Subject: Re: [PATCH v1 2/8] dt-bindings: iio: dac: maxim,ds4424: add
 maxim,rfs-ohms property

On Mon, 19 Jan 2026 18:27:52 +0000
Conor Dooley <conor@...nel.org> wrote:

> On Mon, Jan 19, 2026 at 07:24:18PM +0100, Oleksij Rempel wrote:
> > Introduce the 'maxim,rfs-ohms' property. The full-scale output current
> > of these DACs is determined by external resistors (Rfs) connected to
> > the FS pins. The driver requires the physical resistance values to
> > calculate the correct current scale (Amps per step) for the IIO
> > subsystem.
> > 
> > Keep it optional to avoid forcing updates of existing DTs; without it
> > the driver cannot derive a correct IIO scale.  
> 
> I don't really follow the logic here, if the driver doesn't work
> properly without it, shouldn't it be a required property even if that
> means existing devicetrees get new warnings? Warnings are preferable to
> the drivers malfunctioning on those devices, after all!

Agreed. The driver can paper over holes or I guess we could provide a default
if the datasheet has some reference value or similar?  

DT binding should require it.

> 
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > ---
> >  .../devicetree/bindings/iio/dac/maxim,ds4424.yaml     | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml b/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
> > index efe63e6cb55d..b7af8464a4fc 100644
> > --- a/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
> > +++ b/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
> > @@ -27,6 +27,17 @@ properties:
> >  
> >    vcc-supply: true
> >  
> > +  maxim,rfs-ohms:
> > +    description: |
> > +      Array of resistance values in Ohms for the external Rfs resistors
> > +      connected to the FS pins.
> > +      - For DS44x2 (2 channels): 2 values required.
> > +      - For DS44x4 (4 channels): 4 values required.
> > +      Typical values range from 40000 (40 kOhm) to 160000 (160 kOhm).
> > +    minItems: 2
> > +    maxItems: 4
> > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > +
> >  required:
> >    - compatible
> >    - reg
> > -- 
> > 2.47.3
> >