Re: [PATCH v4 1/2] dt-bindings: iio: adc: Add MAX1241 device tree bindings in documentation

["Ardelean, Alexandru" <alexandru.Ardelean@analog.com>]

On Sat, 2020-03-21 at 21:35 +0200, Alexandru Lazar wrote:
> Hi Jonathan,
> 
> > Please consider also adding the vdd-supply.
> > It's not really required, but if you don't add it from the start
> > chances are high that at some point someone else will need to
> > add it.
> 
> Sorry if I'm missing something obvious here -- what vdd-supply is
> that? Are you thinking of the regulator used for the ADC's reference
> voltage? That's already there (vref-supply).
> 
> Or did you mean I should add a definition for the regulator output used
> for the device's Vdd input (i.e. the positive supply voltage)? Needless
> to say, I'm happy to add it if you think it's a good idea. It's just I
> don't think I've seen it in other drivers (except maybe ad7192?) -- so I
> figured I'd ask before sending a botched v5.
> 

Yep.
Jonathan refers to Vdd input/pin [on the chip] which is different from Vref [REF
pin].
Not all drivers define Vdd.
Some call it AVdd.

You can check via:  git grep -i vdd | cut -d: -f1 | sort | uniq -c
in the drivers/iio folder 

It's an idea to add it, and that can give control to the driver to power-up the
ADC, by defining a regulator [vdd-supply] in the device-tree.

Maybe it could be interesting to move this to the IIO core as an option-flag.
[But that's another discussion]

> Best regards,
> Alex
> 
> > One trivial thing inline.  Otherwise looks good to me.
> > 
> > > ---
> > >  .../bindings/iio/adc/maxim,max1241.yaml       | 61 +++++++++++++++++++
> > >  1 file changed, 61 insertions(+)
> > >  create mode 100644
> > > Documentation/devicetree/bindings/iio/adc/maxim,max1241.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/iio/adc/maxim,max1241.yaml
> > > b/Documentation/devicetree/bindings/iio/adc/maxim,max1241.yaml
> > > new file mode 100644
> > > index 000000000000..de41d422ce3b
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/iio/adc/maxim,max1241.yaml
> > > @@ -0,0 +1,61 @@
> > > +# SPDX-License-Identifier: GPL-2.0
> > > +# Copyright 2020 Ioan-Alexandru Lazar
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/iio/adc/maxim,max1241.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Maxim MAX1241 12-bit, single-channel analog to digital converter
> > > +
> > > +maintainers:
> > > +  - Ioan-Alexandru Lazar <alazar@startmail.com>
> > > +
> > > +description: |
> > > +  Bindings for the max1241 12-bit, single-channel ADC device. This
> > > +  driver supports voltage reading and can optionally be configured for
> > 
> > Driver shouldn't be mentioned in the binding. It's a description of the
> > hardware only.
> > 
> > > +  power-down mode operation. The datasheet can be found at:
> > > +    https://datasheets.maximintegrated.com/en/ds/MAX1240-MAX1241.pdf
> > > +
> > > +properties:
> > > +  compatible:
> > > +    enum:
> > > +      - maxim,max1241
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  vref-supply:
> > > +    description:
> > > +      Device tree identifier of the regulator that provides the external
> > > +      reference voltage.
> > > +    maxItems: 1
> > > +
> > > +  shdn-gpios:
> > > +    description:
> > > +      GPIO spec for the GPIO pin connected to the ADC's /SHDN pin. If
> > > +      specified, the /SHDN pin will be asserted between conversions,
> > > +      thus enabling power-down mode.
> > > +    maxItems: 1
> > > +
> > > +required:
> > > +  - compatible
> > > +  - reg
> > > +  - vref-supply
> > > +
> > > +examples:
> > > +  - |
> > > +    #include <dt-bindings/gpio/gpio.h>
> > > +    spi0 {
> > > +      #address-cells = <1>;
> > > +      #size-cells = <0>;
> > > +
> > > +        adc@0 {
> > > +            compatible = "maxim,max1241";
> > > +            reg = <0>;
> > > +            vref-supply = <&vdd_3v3_reg>;
> > > +            spi-max-frequency = <1000000>;
> > > +            shdn-gpios = <&gpio 26 1>;
> > > +        };
> > > +    };
> > > +
> > > +