linux-kernel - Re: [PATCH v3 1/2] dt-bindings: iio: adf4371: add rdiv2 and doubler

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Message-ID: <20241205-tummy-snorkel-2765ce63dc3f@spud>
Date: Thu, 5 Dec 2024 18:14:59 +0000
From: Conor Dooley <conor@...nel.org>
To: "Miclaus, Antoniu" <Antoniu.Miclaus@...log.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	"robh@...nel.org" <robh@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] dt-bindings: iio: adf4371: add rdiv2 and doubler

On Mon, Dec 02, 2024 at 09:47:21AM +0000, Miclaus, Antoniu wrote:

> > -----Original Message-----
> > From: Jonathan Cameron <jic23@...nel.org>
> > Sent: Saturday, November 30, 2024 6:40 PM
> > To: Miclaus, Antoniu <Antoniu.Miclaus@...log.com>
> > Cc: robh@...nel.org; conor+dt@...nel.org; linux-iio@...r.kernel.org;
> > devicetree@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> > pwm@...r.kernel.org
> > Subject: Re: [PATCH v3 1/2] dt-bindings: iio: adf4371: add rdiv2 and doubler
> > 
> > [External]
> > 
> > On Fri, 29 Nov 2024 17:33:52 +0200
> > Antoniu Miclaus <antoniu.miclaus@...log.com> wrote:
> > 
> > > Add support for reference doubler enable and reference divide by 2
> > > clock.
> > >
> > > Both of these blocks are optional on the frequency path within the
> > > chip and can be adjusted depending on the custom needs of the
> > > applications.
> > Thanks for the additional info!
> > >
> > > The doubler is useful for increasing the PFD comparison frequency
> > > which will result in a noise performance of the system.
> > 
> > So I'll play devil's advocate. Improved noise performance sounds
> > good. If it doesn't take me out of range of allowed frequencies, why
> > would I not turn it on?  What is it about the surrounding circuitry
> > etc that would make this a bad idea for some uses of this chip
> > but not others?

Did I miss a response to this?

> > > The reference divide by 2 divides the reference signal by 2,
> > > resulting in a 50% duty cycle PFD frequency.
> > 
> > why would I want one of those? My 'guess' is this makes sense
> > if the reference frequency is too high after the application of
> > the scaling done by the 5 bit counter.  In effect it means the
> > division circuitry does divide by 1-31, 2-64 in steps of 2.
> > 
> > That could all be wrapped up in the existing control of the
> > frequency, and so far I'm still not seeing a strong reason why
> > it belongs in DT.
> > 
> > The 50% cycle thing is a bit of a red herring as assuming it
> > is triggered on say the rising edge of the high frequency signal
> > to toggle the divided signal, that will always be a 50% duty cycle.
> > 
> As mentioned in the cover letter this was mostly a request from
> customers that are using adf4371 on a large scale and they need
> these features to be controllable somehow by the user.
> 
> Since these attributes were already validated as devicetree properties
> for adf4350 on mainline, I found this as the best approach to satisfy
> both ends.

Probably shouldn't have allowed it then, but things were different a
decade ago.

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