Message-ID: <20240118-freebase-uptake-ec5fdf786d20@spud>
Date: Thu, 18 Jan 2024 16:06:29 +0000
From: Conor Dooley <conor@...nel.org>
To: Ceclan Dumitru <mitrutzceclan@...il.com>
Cc: linus.walleij@...aro.org, brgl@...ev.pl, andy@...nel.org,
	linux-gpio@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
	Jonathan Cameron <jic23@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Michael Walle <michael@...le.cc>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Arnd Bergmann <arnd@...db.de>, ChiaEn Wu <chiaen_wu@...htek.com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Leonard Göhrs <l.goehrs@...gutronix.de>,
	Mike Looijmans <mike.looijmans@...ic.nl>,
	Haibo Chen <haibo.chen@....com>,
	Hugo Villeneuve <hvilleneuve@...onoff.com>,
	David Lechner <dlechner@...libre.com>,
	Ceclan Dumitru <dumitru.ceclan@...log.com>,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 1/2] dt-bindings: adc: add AD7173

On Thu, Jan 18, 2024 at 05:51:20PM +0200, Ceclan Dumitru wrote:
> 
> 
> On 1/18/24 17:23, Conor Dooley wrote:
> > On Thu, Jan 18, 2024 at 02:49:22PM +0200, Dumitru Ceclan wrote:
> 
> ...
> 
> >> +  adi,clock-select:
> >> +    description: |
> >> +      Select the ADC clock source. Valid values are:
> >> +      int         : Internal oscillator
> >> +      int-out     : Internal oscillator with output on XTAL2 pin
> >> +      ext-clk     : External clock input on XTAL2 pin
> >> +      xtal        : External crystal on XTAL1 and XTAL2 pins
> >> +
> >> +    $ref: /schemas/types.yaml#/definitions/string
> >> +    enum:
> >> +      - int
> >> +      - int-out
> >> +      - ext-clk
> >> +      - xtal
> >> +    default: int
> > I am not a fan of properties like this one, that in my view reimplement
> > things that are supported by the regular clocks properties. I've got
> > some questions for you so I can understand whether or not this custom
> > property is required.
> > 
> > Whether or not the ext-clk or xtal is used is known based on
> > clock-names - why is the custom property required to determine that?

> > If neither of those clocks are present, then the internal clock would be
> > used. Choosing to use the internal clock if an external one is provided
> > sounds to me like a software policy decision made by the operating
> > system.
> 
> If there was no int-out, sure. I considered that the choice between int
> and int-out could be made here. So better for driver to choose int/int-out?

This part of my comments was specifically about choosing between use of
the internal clock when ext-clk or xtal are provided, which I think
excludes the possibility of using int-out, since the XTAL2 pin is an
input.

There's 3 situations:
- no external clock provided
- ext-clk provided
- xtal provided

For the former, you know you're in that state when no "clocks" property
is present. The latter two you can differentiate based on "clock-names".

Choosing to use the internal clock if an external clock is provided
seems to be a software policy decision, unless I am mistaken.

> > 
> > Finally, if the ADC has a clock output, why can that not be represented
> > by making the ADC a clock-controller?
> > 
> 
> Was not familiar with this/did not cross my mind. So if xtal/ext-clk is
> present, the driver should detect it and disable the option for clock
> output? (Common pin XTAL2)

Yeah, if those clocks are provided you would not register as a clock
controller. If there is a user of the output clock, it should have its
own "clocks" property that references the ADC's output.

Your dt-binding could also make clocks/clock-names & clock-controller
mutually exclusive.

Cheers,
Conor.

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