linux-kernel - Re: [PATCH v4 01/11] dt-bindings: iio: adc: Add AD4170

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Message-ID: <20250609164425.00007a13@huawei.com>
Date: Mon, 9 Jun 2025 16:44:25 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
CC: Jonathan Cameron <jic23@...nel.org>, Marcelo Schmitt
	<marcelo.schmitt@...log.com>, <linux-iio@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <lars@...afoo.de>,
	<Michael.Hennerich@...log.com>, <dlechner@...libre.com>,
	<nuno.sa@...log.com>, <andy@...nel.org>, <robh@...nel.org>,
	<krzk+dt@...nel.org>, <conor+dt@...nel.org>, <linus.walleij@...aro.org>,
	<brgl@...ev.pl>
Subject: Re: [PATCH v4 01/11] dt-bindings: iio: adc: Add AD4170

On Mon, 9 Jun 2025 12:28:57 -0300
Marcelo Schmitt <marcelo.schmitt1@...il.com> wrote:

> On 06/07, Jonathan Cameron wrote:
> > On Mon, 2 Jun 2025 08:36:24 -0300
> > Marcelo Schmitt <marcelo.schmitt@...log.com> wrote:
> >   
> > > Add device tree documentation for AD4170 and similar sigma-delta ADCs.
> > > The AD4170 is a 24-bit, multichannel, sigma-delta ADC.
> > >   
> ...
> > > +
> > > +$defs:
> > > +  reference-buffer:
> > > +    description: |
> > > +      Enable precharge buffer, full buffer, or skip reference buffering of
> > > +      the positive/negative voltage reference. Because the output impedance
> > > +      of the source driving the voltage reference inputs may be dynamic, RC  
> > 
> > RC?  
> 
> Stands for the combination of resistive and capacitive elements in the path
> between the reference supply output and AD4170 REFINn± inputs.

Ah.  My head wasn't in the right space at all. RC is common enough term but
I'd still spell it out here as DC is very near as is ADC and the C is different
in all 3 cases :)

resistance/capacitance (RC)

or something along those lines should do the job.


> 
> Datasheet Figure 76 shows an example with only capacitive elements, but it could
> have resistive elements too.
> https://www.analog.com/media/en/technical-documentation/data-sheets/ad4170-4.pdf#unique_75_Connect_42_ID8013
> 
> I will rephrase to make that clearer. This is probably too long and detailed
> description for a dt property. I can't figure out how to put that in a more
> concise and meaningful way, though. 
> 
> >   
> > > +      combinations of those inputs can cause DC gain errors if the reference
> > > +      inputs go unbuffered into the ADC. Enable reference buffering if the
> > > +      provided reference source has dynamic high impedance output. Note the
> > > +      absolute voltage allowed on REFINn+ and REFINn- inputs is from
> > > +      AVSS - 50 mV to AVDD + 50 mV when the reference buffers are disabled
> > > +      but narrows to AVSS to AVDD when reference buffering is enabled or in
> > > +      precharge mode. The valid options for this property are:
> > > +      0: Reference precharge buffer.
> > > +      1: Full reference buffering.
> > > +      2: Bypass reference buffers (buffering disabled).
> > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > +    enum: [0, 1, 2]
> > > +    default: 1  
> >   
> ...
> > > +
> > > +      adi,excitation-current-0-microamp:
> > > +        description:
> > > +          Excitation current in microamperes to be applied to pin specified in
> > > +          adi,excitation-pin-0 while this channel is active.
> > > +        enum: [0, 10, 50, 100, 250, 500, 1000, 1500]  
> > 
> > What motivated mix of using $ref and here where there is a lot of repetition?
> > I don't mind which approach is used, but a mix seems the worst option.
> >   
> 
> Because 
> $defs:
>   ...
>   adi,excitation-current-n-microamp:
>     description:
>       Excitation current in microamperes to be applied to pin specified in
>       adi,excitation-pin-0 while this channel is active.
>     enum: [0, 10, 50, 100, 250, 500, 1000, 1500]
>     default: 0
> 
> patternProperties:
>   ...
>       adi,excitation-current-0-microamp:
>         $ref: '#/$defs/adi,excitation-current-n-microamp'
> 
> 
> triggers dt_binding_check warn:
> 	patternProperties:^channel@[0-9a-f]$:properties:adi,excitation-current-0-microamp: '$ref' should not be valid under {'const': '$ref'}
> 	hint: Standard unit suffix properties don't need a type $ref
Fair enough!

J
> 
> 
> Thanks,
> Marcelo
>