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

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Message-ID: <20260122193312.0a84ac33@jic23-huawei>
Date: Thu, 22 Jan 2026 19:33:12 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>, Rodrigo Alencar 
 <455.rodrigo.alencar@...il.com>, 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, 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, 21 Jan 2026 14:21:00 +0000
Nuno Sá <noname.nuno@...il.com> wrote:

> On Wed, 2026-01-21 at 11:52 +0200, Andy Shevchenko wrote:
> > 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.  
> 
> Agreed!
> 
> >   
> > > > (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.  
> 
> 
> Fine with me.
Likewise. A common / foundational function with specialized wrappers would
be good.

> 
> - Nuno Sá
>