linux-kernel - Re: [PATCH v1 01/15] dt-bindings: iio: adc: ad7768-1: add synchronization over SPI property

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Message-ID: <20250112120530.1950a265@jic23-huawei>
Date: Sun, 12 Jan 2025 12:05:30 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, lars@...afoo.de,
 Michael.Hennerich@...log.com, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org
Subject: Re: [PATCH v1 01/15] dt-bindings: iio: adc: ad7768-1: add
 synchronization over SPI property

On Fri, 10 Jan 2025 18:51:06 -0300
Marcelo Schmitt <marcelo.schmitt1@...il.com> wrote:

> On 01/07, Jonathan Santos wrote:
> > Add adi,sync-in-spi property to enable synchronization over SPI.
> > This should be used in the case when the GPIO cannot provide a
> > pulse synchronous with the base MCLK signal.
> > 
> > User can choose between SPI, GPIO synchronization or neither of them,
> > but only if a external pulse can be provided, for example, by another
> > device in a multidevice setup.
> > 
> > Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> > ---
> >  .../bindings/iio/adc/adi,ad7768-1.yaml        | 24 ++++++++++++++++++-
> >  1 file changed, 23 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> > index 3ce59d4d065f..55cec27bfe60 100644
> > --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> > +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> > @@ -47,6 +47,15 @@ properties:
> >        in any way, for example if the filter decimation rate changes.
> >        As the line is active low, it should be marked GPIO_ACTIVE_LOW.
> >  
> > +  adi,sync-in-spi:
> > +    description:
> > +      Enables synchronization of multiple devices over SPI. This property is
> > +      used when a signal synchronous to the base MCLK signal cannot be provided
> > +      via GPIO. It requires the SYNC_OUT pin to be connected to the SYNC_IN pin
> > +      on the ADC. In the case of multiple devices, the SYNC_OUT pin of one device
> > +      should be routed to the SYNC_IN pins of the other devices.  
> So, if I'm getting it right,

Datasheet on this is indeed complex!

>/SYNC_IN may be driven by a GPIO (ADAQ7768-1 datasheet Figure 131),

For that we expose a gpio binding already. If that's present we know what is going on.

>/SYNC_IN may be driven by own device /SYNC_OUT (ADAQ7768-1 datasheet Figure 133),

This is the default - no information provided so it isn't wired externally.
We don't normally bother to describe required chip to chip connections.
I couldn't entirely figure out if this is 'required' if we aren't driving explicitly
from GPIO or another chip but i think it is(?).

>/SYNC_IN may be driven by other AD7768-1 > /SYNC_OUT pin (also Figure 133).
This is only case we are about for sync in I think.

As long as there isn't a valid 'not connected' It think we are fine with a boolean.

> That is too much to describe with a boolean.
> 
> If David's suggestion of using a trigger-source doesn't fit, this property
> should at least become an enum or string.
> 
> > +    type: boolean
> > +
> >    reset-gpios:
> >      maxItems: 1
> >  
> > @@ -65,7 +74,6 @@ required:
> >    - vref-supply
> >    - spi-cpol
> >    - spi-cpha
> > -  - adi,sync-in-gpios
> >  
> >  patternProperties:
> >    "^channel@([0-9]|1[0-5])$":
> > @@ -89,6 +97,20 @@ patternProperties:
> >  allOf:
> >    - $ref: /schemas/spi/spi-peripheral-props.yaml#
> >  
> > +  # adi,sync-in-gpios and adi,sync-in-spi are mutually exclusive (neither is also valid)
> > +  - if:
> > +      required:
> > +        - adi,sync-in-gpios
> > +    then:
> > +      properties:
> > +        adi,sync-in-spi: false
> > +  - if:
> > +      required:
> > +        - adi,sync-in-spi
> > +    then:
> > +      properties:
> > +        adi,sync-in-gpios: false
> > +
> >  unevaluatedProperties: false
> >  
> >  examples:
> > -- 
> > 2.34.1
> >