netdev - Re: [RFC PATCH v7 1/8] dpll: spec: Add Netlink spec in YAML

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Message-ID: <20230511162926.009994bb@kernel.org>
Date: Thu, 11 May 2023 16:29:26 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "Kubalewski, Arkadiusz" <arkadiusz.kubalewski@...el.com>
Cc: Vadim Fedorenko <vadfed@...a.com>, Jiri Pirko <jiri@...nulli.us>,
 Jonathan Lemon <jonathan.lemon@...il.com>, Paolo Abeni <pabeni@...hat.com>,
 "Olech, Milena" <milena.olech@...el.com>, "Michalik, Michal"
 <michal.michalik@...el.com>, "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>, poros <poros@...hat.com>, mschmidt
 <mschmidt@...hat.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>, Vadim Fedorenko
 <vadim.fedorenko@...ux.dev>
Subject: Re: [RFC PATCH v7 1/8] dpll: spec: Add Netlink spec in YAML

On Thu, 11 May 2023 20:53:40 +0000 Kubalewski, Arkadiusz wrote:
> >Because I think that'd be done by an NCO, no?  
> 
> From docs I can also see that chip has additional designated dpll for NCO mode,
> and this statement:
> "Numerically controlled oscillator (NCO) behavior allows system software to steer
> DPLL frequency or synthesizer frequency with resolution better than 0.005 ppt."
> 
> I am certainly not an expert on this, but seems like the NCO mode for this chip
> is better than FREERUN, since signal produced on output is somehow higher quality.

Herm, this seems complicated. Do you have a use case for this? 
Maybe we can skip it :D

My reading of the quote is that there is an NCO which SW can control
precisely. But that does not answer the questions:
 - is the NCO driven by system clock or can it be used in locked mode?
 - what is the "system software"? FW which based on temperature
   information, and whatever else compensates drift of system clock?
   or there are exposed registers to control the NCO?