linux-kernel - Re: [PATCH v7 5/6] dt-bindings: iio: adc: ad7192: Add AD7194 support

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Date: Fri, 10 May 2024 09:21:37 -0500
From: David Lechner <dlechner@...libre.com>
To: Alisa-Dariana Roman <alisadariana@...il.com>,
 Conor Dooley <conor@...nel.org>
Cc: michael.hennerich@...log.com, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 alexandru.tachici@...log.com, lars@...afoo.de, jic23@...nel.org,
 robh@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 lgirdwood@...il.com, broonie@...nel.org, andy@...nel.org,
 nuno.sa@...log.com, marcelo.schmitt@...log.com, bigunclemax@...il.com,
 okan.sahin@...log.com, fr0st61te@...il.com, alisa.roman@...log.com,
 marcus.folkesson@...il.com, schnelle@...ux.ibm.com, liambeguin@...il.com
Subject: Re: [PATCH v7 5/6] dt-bindings: iio: adc: ad7192: Add AD7194 support

On 5/10/24 5:05 AM, Alisa-Dariana Roman wrote:
> On 30.04.2024 20:21, Conor Dooley wrote:
>> On Tue, Apr 30, 2024 at 07:29:45PM +0300, Alisa-Dariana Roman wrote:
>>> +      diff-channels:
>>> +        description:
>>> +          Both inputs can be connected to pins AIN1 to AIN16 by choosing the
>>> +          appropriate value from 1 to 16.
>>> +        items:
>>> +          minimum: 1
>>> +          maximum: 16
>>> +
>>> +      single-channel:
>>> +        description:
>>> +          Positive input can be connected to pins AIN1 to AIN16 by choosing the
>>> +          appropriate value from 1 to 16. Negative input is connected to AINCOM.
>>> +        items:
>>> +          minimum: 1
>>> +          maximum: 16
>>
>> Up to 16 differential channels and 16 single-ended channels, but only 16
>> pins? Would the number of differential channels not max out at 8?
> 
> Hello, Conor! I really appreciate the feedback!
> 
> The way I thought about it, the only thing constraining the number of channels is the reg number (minimum: 0, maximum: 271). 272 channels cover all possible combinations (16*16 differential and 16 single ended) and I thought there is no need for anything stricter. I added items: minimum:1 maximum:16 to make sure the numbers are from 1 to 16, corresponding to AIN1-AIN16.
> 
> Please let me know what should be improved!
> 
> Kind regards,
> Alisa-Dariana Roman.
> 

Having looked at the datasheet for this and other similar chips, I agree
that this reasoning makes sense. Some of the similar chips that have fixed
channel assignments still have, e.g. a channel where + and - are both
AIN2 (I assume for diagnostics). So I think it makes sense to allow for
doing something similar here even if the most common use cases will
probably have at most 16 channels defined in the .dts.