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

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Date: Thu, 27 Jun 2024 17:13:16 +0100
From: Conor Dooley <conor@...nel.org>
To: Olivier MOYSAN <olivier.moysan@...s.st.com>
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

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?

Thanks,
Conor.

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