linux-kernel - Re: [PATCH v2 1/4] dt-bindings: iio: adc: ad7192: Add properties

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Date: Fri, 2 Feb 2024 16:20:10 -0600
From: David Lechner <dlechner@...libre.com>
To: Alisa-Dariana Roman <alisadariana@...il.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, 
	Alisa-Dariana Roman <alisa.roman@...log.com>, Michael Hennerich <michael.hennerich@...log.com>, 
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>, 
	Alexandru Tachici <alexandru.tachici@...log.com>, Jonathan Cameron <jic23@...nel.org>, 
	Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Ceclan Dumitru <dumitru.ceclan@...log.com>
Subject: Re: [PATCH v2 1/4] dt-bindings: iio: adc: ad7192: Add properties

On Fri, Feb 2, 2024 at 8:14 AM Alisa-Dariana Roman
<alisadariana@...il.com> wrote:
>
> On 14.11.2023 22:29, Krzysztof Kozlowski wrote:
> > On 14/11/2023 21:05, Alisa-Dariana Roman wrote:
> >> Document properties used for clock configuration.
> >
> > Some background here is missing - otherwise it looks like you are adding
> > new properties...
> >
> >>
> >> Signed-off-by: Alisa-Dariana Roman <alisa.roman@...log.com>
> >> ---
> >>   .../devicetree/bindings/iio/adc/adi,ad7192.yaml        | 10 ++++++++++
> >>   1 file changed, 10 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7192.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7192.yaml
> >> index 16def2985ab4..9b59d6eea368 100644
> >> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7192.yaml
> >> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7192.yaml
> >> @@ -80,6 +80,16 @@ properties:
> >>         and when chop is disabled.
> >>       type: boolean
> >>
> >> +  adi,clock-xtal:
> >> +    description: |
> >> +      External crystal connected from MCLK1 to MCLK2.

A better description could be:

When this flag is present, it indicates that the clock from the clocks
property is a crystal oscillator connected to MCLK1 and MCLK2. When
omitted the clock is a CMOS-compatible clock connected to MCLK2.

> >
> > And this should be input clock.
> >
> >> +    type: boolean
> >> +
> >> +  adi,int-clock-output-enable:
> >> +    description: |
> >> +      Internal 4.92 MHz clock available on MCLK2 pin.
> >> +    type: boolean
> >
> > This should be clock-cells and clock provider.
> >
> > Unless you are just documenting already used interface which you do not
> > want to break...

This property is already used in the mainline Linux driver, so sounds
like the "don't want to break it" case. But it would make sense to
deprecate this property and use standard clock provider bindings
instead.

> >
> >> +
> >>     bipolar:
> >>       description: see Documentation/devicetree/bindings/iio/adc/adc.yaml
> >>       type: boolean
> >
> > Best regards,
> > Krzysztof
> >
>
> Thank you very much for the feedback!
>
> If I understand correctly, there is already an input clock in the bindings:
> ```
>    clocks:
>      maxItems: 1
>      description: phandle to the master clock (mclk)
>
>    clock-names:
>      items:
>        - const: mclk
> ```
>
> What I wanted to accomplish with this patch is to document these boolean
> properties (from the ad7192 driver code):
> ```
>         /* use internal clock */
>         if (!st->mclk) {
>                 if (device_property_read_bool(dev, "adi,int-clock-output-enable"))
>                         clock_sel = AD7192_CLK_INT_CO;
>         } else {
>                 if (device_property_read_bool(dev, "adi,clock-xtal"))
>                         clock_sel = AD7192_CLK_EXT_MCLK1_2;
>                 else
>                         clock_sel = AD7192_CLK_EXT_MCLK2;
>         }
> ```
>
> Please let me know how to proceed further!
>
> Kind regards,
> Alisa-Dariana Roman
>

There was another recent discussion about this exact same clock
input/output on another chip recently [1]. So it would be nice if we
could end up with the same bindings in both cases (cc Ceclan). In the
other thread, it was proposed to have the clocks property to be an
array of two phandles, one for the crystal oscillator and one for the
external clock rather than a single clock and the adi,clock-xtal
property. But that would be a breaking change to these bindings.

[1]: https://lore.kernel.org/linux-iio/20240122-bloating-dyslexic-cbc0258c898a@spud/t/#m4e375aa36dae6da0c319518137f03e2f63e72af9