linux-kernel - Re: [PATCH v3 7/8] dt-bindings: iio: adc: adi,ad4030: Add ADAQ4216 and ADAQ4224

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Message-Id: <175892462162.1836299.14644550889187111452.robh@kernel.org>
Date: Fri, 26 Sep 2025 17:10:21 -0500
From: "Rob Herring (Arm)" <robh@...nel.org>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>
Cc: krzk+dt@...nel.org, jic23@...nel.org, conor+dt@...nel.org, 
 corbet@....net, eblanc@...libre.com, devicetree@...r.kernel.org, 
 nuno.sa@...log.com, andy@...nel.org, linux-kernel@...r.kernel.org, 
 michael.hennerich@...log.com, linux-iio@...r.kernel.org, 
 marcelo.schmitt1@...il.com, linux-doc@...r.kernel.org, 
 linux-spi@...r.kernel.org, dlechner@...libre.com
Subject: Re: [PATCH v3 7/8] dt-bindings: iio: adc: adi,ad4030: Add ADAQ4216
 and ADAQ4224


On Fri, 26 Sep 2025 17:40:47 -0300, Marcelo Schmitt wrote:
> ADAQ4216 and ADAQ4224 are similar to AD4030 except that ADAQ devices have a
> PGA (programmable gain amplifier) that scales the input signal prior to it
> reaching the ADC inputs. The PGA is controlled through a couple of pins (A0
> and A1) that set one of four possible signal gain configurations.
> 
> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> ---
> Change log v2 -> v3
> - PGA gain now described in decibels.
> 
> The PGA gain is not going to fit well as a channel property because it may
> affect more than one channel as in AD7191.
> https://www.analog.com/media/en/technical-documentation/data-sheets/AD7191.pdf
> 
> I consulted a very trustworthy source [1, 2] and learned that describing signal
> gains in decibels is a common practice. I now think it would be ideal to describe
> these PGA and PGA-like gains with properties in decibel units and this patch
> is an attempt of doing so. The only problem with this approach is that we end up
> with negative values when the gain is lower than 1 (the signal is attenuated)
> and device tree specification doesn't support signed integer types. As the
> docs being proposed fail dt_binding_check, I guess I have to nack the patch myself.
> Any chance of dt specification eventually support signed integers?
> Any suggestions appreciated.
> 
> [1] https://en.wikipedia.org/wiki/Decibel
> [2] https://en.wikipedia.org/wiki/Gain_(electronics)
> 
> Thanks,
> Marcelo
> 
>  .../bindings/iio/adc/adi,ad4030.yaml          | 84 +++++++++++++++++--
>  1 file changed, 79 insertions(+), 5 deletions(-)
> 

My bot found errors running 'make dt_binding_check' on your patch:

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Error: Documentation/devicetree/bindings/iio/adc/adi,ad4030.example.dts:68.36-37 syntax error
FATAL ERROR: Unable to parse input tree
make[2]: *** [scripts/Makefile.dtbs:131: Documentation/devicetree/bindings/iio/adc/adi,ad4030.example.dtb] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/builds/robherring/dt-review-ci/linux/Makefile:1527: dt_binding_check] Error 2
make: *** [Makefile:248: __sub-make] Error 2

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/5dc08b622dac1db561f26034c93910ccff75e965.1758916484.git.marcelo.schmitt@analog.com

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.