linux-kernel - Re: [PATCH 2/2] iio: adc: ad9467: make iio backend optional

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Message-ID: <c3ed08159082c15f8804c6963b4422bbbf2039ab.camel@gmail.com>
Date: Wed, 17 Dec 2025 09:26:10 +0000
From: Nuno Sá <noname.nuno@...il.com>
To: Tomas Melin <tomas.melin@...sala.com>, Michael Hennerich	
 <Michael.Hennerich@...log.com>, Nuno Sa <nuno.sa@...log.com>, Lars-Peter
 Clausen <lars@...afoo.de>, Jonathan Cameron <jic23@...nel.org>, David
 Lechner	 <dlechner@...libre.com>, Andy Shevchenko <andy@...nel.org>
Cc: "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>, 
 "linux-kernel@...r.kernel.org"
	 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] iio: adc: ad9467: make iio backend optional

On Tue, 2025-12-16 at 15:39 +0000, Tomas Melin wrote:
> Hi,
> 
> On 16/12/2025 14:56, Nuno Sá wrote:
> > On Tue, 2025-12-16 at 11:40 +0000, Tomas Melin wrote:
> > > Not all users can or want to use the device with an iio-backend.
> > > For these users, let the driver work in standalone mode, not coupled
> > > to the backend or the services it provides.
> > > 
> > > Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
> > > ---
> > 
> > Which users? The only usecases (for all the supported devices) we have require
> > the FPGA backend. So do you have a specific usecase for a specific device? If so, I would
> > prefer an explicit boolean in the chip_info struture for the device(s) we know this
> > can happen (unless you have a usecase for all :)).
> 
> This is generically for all the devices supported by the ad9467, not
> only a specific device. So it's about how this is used as part of the
> design.
> 
> This is aimed at users that do not use the ADI HDL reference backend
> with these devices, but instead have custom backends suited for their
> own needs.

Hmm, ideally I would then like to see the backend driver upstreamed...

> In that case, we need to be able to skip the backend registration and
> register device as a standalone iio device.
> 
> Hopefully this made the use case clearer?
> 

I mean, I don't love this and I'm not really sure I'm ok with it. These are fairly
high speed devices which often do require an FPGA IP to handle the data flow. Now
we can ignore the backend device (which is an essential piece) being it
expected or not.

Or maybe we can just do something like regulators and get a dummy backend or just add
some fixed kind of backend. Bottom line is, it still seems the backend device is a core
piece in your design and we're just hacking around the driver in way that conceptually
doesn't make sense to me.

Other question that comes to mind (I guess I was not that clear)... Do you have a real
usecase with your own custom backend IP or is this just theoretical?

- Nuno Sá