linux-kernel - Re: [PATCH 2/6] dt-bindings: iio: dac: ad5791: Add required voltage supplies

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Message-ID: <CAKXjFTPwN2TYW6sq1kj3miZ0f5OqKX0aTk8eGf1sj9TBk1_e=A@mail.gmail.com>
Date: Tue, 29 Oct 2024 00:07:19 +0100
From: Axel Haslam <ahaslam@...libre.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org, 
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, nuno.sa@...log.com, 
	dlechner@...libre.com, linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] dt-bindings: iio: dac: ad5791: Add required voltage supplies

On Mon, 28 Oct 2024 at 09:06, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On Mon, Oct 28, 2024 at 08:11:14AM +0100, ahaslam@...libre.com wrote:
> > From: Axel Haslam <ahaslam@...libre.com>
> >
> > Vcc, iovcc, vrefp, and vrefn are needed for the DAC to work.
> > Add them as required bindings for ad5791.
> >
> > Signed-off-by: Axel Haslam <ahaslam@...libre.com>
> > ---
> >  .../bindings/iio/dac/adi,ad5791.yaml          | 24 +++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/iio/dac/adi,ad5791.yaml b/Documentation/devicetree/bindings/iio/dac/adi,ad5791.yaml
> > index fe664378c966..79cb4b78a88a 100644
> > --- a/Documentation/devicetree/bindings/iio/dac/adi,ad5791.yaml
> > +++ b/Documentation/devicetree/bindings/iio/dac/adi,ad5791.yaml
> > @@ -26,6 +26,22 @@ properties:
> >    vdd-supply: true
> >    vss-supply: true
> >
> > +  vcc-supply:
> > +    description:
> > +      Supply that powers the chip.
> > +
> > +  iovcc-supply:
> > +    description:
> > +      Supply for the digital interface.
> > +
> > +  vrefp-supply:
> > +    description:
> > +      Positive referance input voltage range. From 5v to (vdd - 2.5)
> > +
> > +  vrefn-supply:
> > +    description:
> > +      Negative referance input voltage range. From (vss + 2.5) to 0.
> > +
> >    adi,rbuf-gain2-en:
> >      description: Specify to allow an external amplifier to be connected in a
> >        gain of two configuration.
> > @@ -47,6 +63,10 @@ required:
> >    - reg
> >    - vdd-supply
> >    - vss-supply
> > +  - vcc-supply
> > +  - iovcc-supply
> > +  - vrefp-supply
> > +  - vrefn-supply
>
> So you have six required supplies?
>
> Datasheet says "A voltage range of 2.7 V to 5.5 V *can* be connected",
> so doesn't it mean this is optional? Although similar wording is for
> other supplies, so maybe it's just imprecise language?

looks like unfortunate wording. Like you said, Vdd, Vss are already required
and have the same *can* word in their description like all other supplies
which i think its meant for the voltage level options of the power supply.

Vcc:  is mentioned as need to "power on" in the startup sequence
section of the datasheet,
iovcc: we can't interface the chip without this supply.
vrefp: minimum input of 5v.
vrefn: from vss up to 0 volts max.

so vcc, iovcc, and vrefp to me, look required for the hw to work.
but i have a small doubt about vrefn since it could potentially be 0V.
Does this mean it should be an optional binding where we assume its 0
if not present?
or is it ok to leave it as required?

Regards
Axel.


>
> Best regards,
> Krzysztof
>