linux-kernel - Re: [PATCH v4 3/7] iio: frequency: adf41513: driver implementation

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Message-ID: <aXChxvlZxKVrOMsW@smile.fi.intel.com>
Date: Wed, 21 Jan 2026 11:52:06 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Rodrigo Alencar <455.rodrigo.alencar@...il.com>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>, rodrigo.alencar@...log.com,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Andy Shevchenko <andy@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v4 3/7] iio: frequency: adf41513: driver implementation

On Wed, Jan 21, 2026 at 09:41:25AM +0000, Rodrigo Alencar wrote:
> On 26/01/20 03:38PM, Andy Shevchenko wrote:
> > On Tue, Jan 20, 2026 at 01:07:49PM +0000, Rodrigo Alencar wrote:
> > > On 26/01/20 01:24PM, Andy Shevchenko wrote:
> > > > On Tue, Jan 20, 2026 at 12:43 PM Rodrigo Alencar
> > > > <455.rodrigo.alencar@...il.com> wrote:
> > > > > On 26/01/19 07:07PM, Andy Shevchenko wrote:
> > > > > > On Mon, Jan 19, 2026 at 04:37:09PM +0000, Rodrigo Alencar wrote:
> > > > > > > On 26/01/19 03:42PM, Andy Shevchenko wrote:
> > > > > > > > On Mon, Jan 19, 2026 at 11:21:59AM +0000, Rodrigo Alencar wrote:
> > > > > > > > > On 26/01/19 09:31AM, Andy Shevchenko wrote:
> > > > > > > > > > On Fri, Jan 16, 2026 at 02:32:22PM +0000, Rodrigo Alencar via B4 Relay wrote:

...

> > > > > > > > > The current implementation is kind of a stripped version of
> > > > > > > > > __iio_str_to_fixpoint(). Would you prefer something like this, then?:
> > > > > > > >
> > > > > > > > Do they have most of the parts in common? If so, why can't we use
> > > > > > > > __iio_str_to_fixpoint() directly? Or why can't we slightly refactor
> > > > > > > > that to give us the results we need here?
> > > > > > >
> > > > > > > __iio_str_to_fixpoint() only parses "int" chunks, adf41513_parse_uhz
> > > > > > > was modified to accomodate the u64 parsing removing unnecessary stuff.
> > > > > >
> > > > > > But why? The fractional part most likely will be kept int (it's up to 10⁻⁹).
> > > > > > The integer can be bigger than 10⁹?
> > > > >
> > > > > Correct, integer part of the frequency value goes up to 26.5 GHz
> > > > > (uint_max is approx 4.3 GHz). Also, with the dual modulus, the PLL can
> > > > > achieve micro Hz resolution.
> > > > 
> > > > µHz is not a problem since it's up to nHz.
> > > > So, the difference so far is the integer part that can be 64-bit.
> > > > Again, can we factor out something to be used for this and for the
> > > > __iio_str_to_fixpoint() cases?
> > > 
> > > I am not sure what you are suggesting,
> > 
> > To make changes to reuse the code.
> > 
> > > but I am avoiding changes to iio core at this point.
> > 
> > Why?
> 
> I understood that core changes would require more than one user
> supporting the change.

At least one. And we have tons of them as the callers of
__iio_str_to_fixpoint() are not going to disappear. Basically it's a surgery in
the middle of the existing chain of APIs. To me one user is enough justification
for such a surgery. For the newly introduced API (imagine __iio_str_to_fixpoint()
as an example) it's indeed one user not enough.

> > > If any other user needs similar behavior,
> > > I'd say we would need to have __iio_str_to_fixpoint() implementation
> > > modified, so to create a version of iio_str_to_fixpoint() that handles
> > > long long variables. Possibly consuming simple_strtoull instead of
> > > doing the manual parsing.
> > 
> > That's the problem here. With Yet Another Cool Parser this all becomes
> > unmaintainable very soon
> 
> Considering that the need for a new parser for 64-bit parts is only driven
> by this specific PLL driver, I wonder how things become that unmaintainable.

Because there is a duplication of the code (to some extent) and if we found
a bug in the one implementation it will be hard to fix (or even remeber) about
the other.

> > (basically as you said when new comer needs a third
> > variant of it). This is not good. Instead better to create (amend, expand)
> > existing test cases, split out a foundation API that parses 64-bit parts
> > (maybe even for fractional as well, dunno) and evolve a needed (sub)API
> > from it.
> 
> I don't disagree with you though, I suppose I will need a green light to
> move on with this?

Fine with me, let's gather opinions of David, Nuno, Jonathan, and others.

-- 
With Best Regards,
Andy Shevchenko