linux-kernel - Re: [PATCH v2 5/8] dt-bindings: iio: add sigma delta modulator backend

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Date: Wed, 3 Jul 2024 09:06:19 +0200
From: Olivier MOYSAN <olivier.moysan@...s.st.com>
To: Conor Dooley <conor@...nel.org>
CC: <fabrice.gasnier@...s.st.com>, Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, <linux-iio@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/8] dt-bindings: iio: add sigma delta modulator
 backend

Hi Conor,

On 6/27/24 18:13, Conor Dooley wrote:
> On Wed, Jun 26, 2024 at 06:40:58PM +0200, Olivier MOYSAN wrote:
>> Hi Conor,
>>
>> On 6/25/24 17:34, Conor Dooley wrote:
>>> On Tue, Jun 25, 2024 at 05:07:13PM +0200, Olivier Moysan wrote:
>>>> Add documentation of device tree bindings to support
>>>> sigma delta modulator backend in IIO framework.
>>>>
>>>> Signed-off-by: Olivier Moysan <olivier.moysan@...s.st.com>
>>>
>>> I don't review bindings for a job, I can only reliably get to look at
>>> my mail queue in the evenings, please give me a chance to reply to you
>>> before you submit a new version.
>>>
>>
>> Sorry, the short review delay.
>>
>>>> +$id: http://devicetree.org/schemas/iio/adc/sd-modulator-backend.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: Sigma delta modulator backend
>>>
>>> Same comments about filename and title apply here as the previous
>>> version. "TI $foo Sigma Delta Modulator" and drop the reference to back
>>> ends or the pretence of being generic.
>>>
>>
>> The logic here is the same as for the former sigma delta modulator driver.
>> (see discussion [1])
>> I mean introducing a generic and minimalist driver to support sd modulators,
>> but not dedicated to a specific modulator. The ads1201 is chosen as a basic
>> modulator here. But it is rather an arbitrary choice.
>>
>> I agree "backend" reference is not really relevant here. I have to think
>> about a way to manage the coexistence of this sigma delta modulator driver
>> with its former version.
> 
> To be blunt, I don't care about drivers! Well I do, but not in this
> particular context. You can absolutely have a driver that supports
> multiple backends or sigma delta modulators, but right now we are
> talking about a binding and this binding supports exactly one sigma
> delta modulator - and with an explicit compatible. In that context,
> presenting the binding as generic makes little sense.
> 
>> [1] https://lore.kernel.org/all/6943aaf5-b580-0fd1-7a2e-b99f7a266388@st.com/
> 
> Looking at this though, I question the binding more... The programming
> model of the device is identical as a backend or otherwise, so it
> shouldn't be getting a new compatible. Isn't this actually as simple as
> adding #io-backend-cells to the existing binding and using that to
> determine whether the device is being used as a backend or in isolation?
>

For sure. I came to the same conclusion. My first idea was to isolate 
the deprecated binding. But I agree that the best approach is to adapt 
the existing binding. I prepared a v3 like this.

BRs
Olivier

> Thanks,
> Conor.