linux-kernel - Re: [PATCH] dt-bindings: iio: afe: voltage-divider: Add io-channel-cells

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Message-ID: <20240126-blaspheme-calculate-a4134dc1ed68@spud>
Date: Fri, 26 Jan 2024 22:14:03 +0000
From: Conor Dooley <conor@...nel.org>
To: Naresh Solanki <naresh.solanki@...ements.com>
Cc: Peter Rosin <peda@...ntia.se>, Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, mazziesaccount@...il.com,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: iio: afe: voltage-divider: Add
 io-channel-cells

On Fri, Jan 26, 2024 at 11:10:36PM +0530, Naresh Solanki wrote:
> Hi Conor,
> 
> 
> On Fri, 26 Jan 2024 at 22:22, Conor Dooley <conor@...nel.org> wrote:
> >
> > On Fri, Jan 26, 2024 at 09:55:20PM +0530, Naresh Solanki wrote:
> > > On Fri, 26 Jan 2024 at 21:47, Conor Dooley <conor@...nel.org> wrote:
> > > > On Fri, Jan 26, 2024 at 05:25:08PM +0530, Naresh Solanki wrote:
> > > > > Signed-off-by: Naresh Solanki <naresh.solanki@...ements.com>
> > > > > ---
> > > > >  Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml | 3 +++
> > > > >  1 file changed, 3 insertions(+)
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml b/Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml
> > > > > index dddf97b50549..b4b5489ad98e 100644
> > > > > --- a/Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml
> > > > > +++ b/Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml
> > > > > @@ -39,6 +39,9 @@ properties:
> > > > >      description: |
> > > > >        Channel node of a voltage io-channel.
> > > > >
> > > > > +  '#io-channel-cells':
> > > > > +    const: 1
> > > >
> > > > The example in this binding looks like the voltage-divider is intended
> > > > to be an "IIO consumer" but "#io-channels-cells" is an "IIO provider"
> > > > property.
> > > >
> > > > Are you sure this is correct?
> > > I'm not aware that #io-channels-cells is only for IIO provider.
> >
> > #foo-cells properties are always for resource providers
> >
> > > But I do get some kernel message as mention in commit messages
> > > if this is specified in DT.
> >
> > Can you please share the DT in question? Or at least, the section that
> > describes the IIO provider and consumer?
> Below is link to complete DT:
> https://github.com/torvalds/linux/commit/522bf7f2d6b085f69d4538535bfc1eb965632f54

If you're gonna link something that is in a vendor tree, you should link
the actual vendor tree and not something that "does not belong to any
branch on this repository, and may belong to a fork outside of the
repository"!

I did look at what you have there and I think your dts is wrong.

The iio-hwmon binding says:
| description: >
|   Bindings for hardware monitoring devices connected to ADC controllers
|   supporting the Industrial I/O bindings.
| 
|   io-channels:
|     minItems: 1
|     maxItems: 51 # Should be enough
|     description: >
|       List of phandles to ADC channels to read the monitoring values

And then you have:
|	iio-hwmon {
|		compatible = "iio-hwmon";
|		// Voltage sensors top to down
|		io-channels = <&p12v_vd 0>, <&p5v_aux_vd 0>, <&p5v_bmc_aux_vd 0>, <&p3v3_aux_vd 0>,
|			<&p3v3_bmc_aux_vd 0>, <&p1v8_bmc_aux_vd 0>, <&adc1 4>, <&adc0 2>, <&adc1 0>,
|			<&p2V5_aux_vd 0>, <&p3v3_rtc_vd 0>;
|	};
|
|	p12v_vd: voltage_divider1 {
|		compatible = "voltage-divider";
|		io-channels = <&adc1 3>;
|		#io-channel-cells = <1>;
|
|		/* Scale the system voltage by 1127/127 to fit the ADC range.
|		 * Use small nominator to prevent integer overflow.
|		 */
|		output-ohms = <15>;
|		full-ohms = <133>;
|	};

A voltage divider is _not_ an ADC channel, so I don't know why you are
treating it as one in the iio-hwmon entry. Can you explain this please?

Thanks,
Conor.

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