Re: [PATCH v4 02/14] dt-bindings: iio: adc: Add AD7768

[Jonathan Cameron <jic23@kernel.org>]

> > +  ref2p-supply:
> > +    description:
> > +      Positive reference input supply for REF2+. The voltage range is from
> > +      (AVSS + 1 V) to AVDD1. Together, REF2+ and REF2- must provide a
> > +      differential reference voltage from 1 V to |AVDD1 - AVSS|. This
> > +      reference is used by channels 4 to 7 on the AD7768 and channels 2 and 3
> > +      on the AD7768-4.
> > +
> > +  ref2n-supply:
> > +    description:
> > +      Negative reference input supply for REF2-. The voltage range is from
> > +      AVSS to (AVDD1 - 1 V).  
> 
> For all of the supplies, I don't think we need to repeat so much of what the
> datasheet says. It is getting quite noisy and makes it hard to see the parts
> of the description that are actually relevant to how the devicetree is to be
> interpreted. (includes VCM as well)

Agreed.  Keep anything about how being present / not present may matter.
Pretty much anything else isn't really that interesting.
Sometimes
	xxx-supply: true

is enough.

> 
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> > +    description: GPIO connected to the active-low RESET pin
> > +
> > +  start-gpios:
> > +    maxItems: 1
> > +    description:
> > +      GPIO connected to the START pin. An active-low pulse on this pin
> > +      synchronizes the device to other AD7768 devices. When not used, this
> > +      pin must be tied to a logic high level through a pull-up resistor.
> > +      When used, SYNC_OUT must be wired back to SYNC_IN on all devices in
> > +      the synchronization chain.
> > +
> > +  sync-in-gpios:
> > +    maxItems: 1
> > +    description:
> > +      GPIO connected to the SYNC_IN pin. Receives the synchronization pulse
> > +      generated on SYNC_OUT in response to a START pulse. Must be synchronous
> > +      to the MCLK clock domain. In multi-device or daisy-chained systems,
> > +      two successive synchronization pulses must be applied to guarantee all
> > +      ADCs are synchronized.
> > +
> > +  sync-out-gpios:  
> 
> Unusual to have an output pin connected to a GPIO. Usually this would be an
> interrupt or trigger-sources.
> 
> > +    maxItems: 1
> > +    description:
> > +      GPIO connected to the SYNC_OUT pin. Outputs a synchronization pulse
> > +      synchronous to MCLK in response to a START pulse or SPI_SYNC command.
> > +      In single-device configurations this pin must be wired back to SYNC_IN.
> > +      In multi-device configurations it can be routed to the SYNC_IN pins of
> > +      all devices in the chain.  
> 
> Although this description makes it sounds like the SYNC_OUT pin is only ever
> wired to SYNC_IN. So wouldn't be described here at all.

We don't have a particularly good way to say "this hardware controlled pin
is wired from this ADC to this second ADC"  As you note though GPIO doesn't
work for that.