linux-kernel - Re: [PATCH v2 2/6] dt-bindings: iio: amplifiers: Add AD8366 support

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Message-ID: <20260128-grieving-polish-4292db90090d@spud>
Date: Wed, 28 Jan 2026 14:43:20 +0000
From: Conor Dooley <conor@...nel.org>
To: Rodrigo Alencar <455.rodrigo.alencar@...il.com>
Cc: rodrigo.alencar@...log.com, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>
Subject: Re: [PATCH v2 2/6] dt-bindings: iio: amplifiers: Add AD8366 support

On Wed, Jan 28, 2026 at 09:39:12AM +0000, Rodrigo Alencar wrote:
> On 26/01/27 07:38PM, Conor Dooley wrote:
> > On Tue, Jan 27, 2026 at 11:37:52AM +0000, Rodrigo Alencar wrote:
> > > On 26/01/26 08:11PM, Conor Dooley wrote:
> > > > On Mon, Jan 26, 2026 at 01:51:03PM +0000, Rodrigo Alencar via B4 Relay wrote:
> > > > > From: Rodrigo Alencar <rodrigo.alencar@...log.com>
> > > > > 
> > > > > Add device tree binding documentation for amplifiers and digital
> > > > > attenuators. This covers different device variants with similar
> > > > > SPI control.
> > > 
> > > ...
> > > 
> > > > > +properties:
> > > > > +  compatible:
> > > > > +    enum:
> > > > > +      - adi,ad8366
> > > > > +      - adi,ada4961
> > > > > +      - adi,adl5240
> > > > > +      - adi,adrf5720
> > > > > +      - adi,adrf5730
> > > > > +      - adi,adrf5731
> > > > > +      - adi,hmc271a
> > > > > +      - adi,hmc792a
> > > > > +      - adi,hmc1018a
> > > > > +      - adi,hmc1019a
> > > > > +      - adi,hmc1119
> > > > 
> > > > Why do none of these devices use fallback compatibles? Please put the
> > > > rationale in the commit message.
> > > 
> > > Will do. Each device has their own gain range/step. 
> > > 
> > > > > +
> > > > > +  reg:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  vcc-supply:
> > > > > +    description: Regulator that provides power to the device.
> > > > > +
> > > > > +  reset-gpios:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  enable-gpios:
> > > > > +    maxItems: 1
> > > > 
> > > > How come enable-gpios is optional? Is it optional on all devices?
> > > > Do all devices support enable-gpios and/or reset-gpios?
> > > 
> > > Board designs often hardwire powerup or serial mode enable signals
> > > to high voltage level, so there will not be a reason to add the
> > > enable-gpio.
> > 
> > I don't see anything about all devices supporting enable-gpios, adl5240
> > doesn't appear to have one? I'm not going to check all of the datasheets
> > to see about the others, but you should disallow the property on devices
> > that don't have an enable pin.
> 
> Understood. I will prepare the following for v3:
> 
> allOf:
>   - $ref: /schemas/spi/spi-peripheral-props.yaml#
>   - if:
>       properties:
>         compatible:
>           contains:
>             const: adi,hmc271a
>     then:
>       properties:
>         reset-gpios:
>           maxItems: 1

This doesn't look right. The stuff you currently have in the patch
should remain, and this should become
if:
  properties:
    compatible:
      not:
        contains:
          const: adi,hmc271a
then:
  properties:
    reset-gpios: false

>   - if:
>       properties:
>         compatible:
>           contains:
>             anyOf:
>               - const: adi,ad8366
>               - const: adi,ada4961
>               - const: adi,adrf5720
>               - const: adi,adrf5730
>               - const: adi,adrf5731
>               - const: adi,hmc792a
>               - const: adi,hmc1018a
>               - const: adi,hmc1019a
>               - const: adi,hmc1119
>     then:
>       properties:
>         enable-gpios:
>           maxItems: 1
>           description: Power-up or Serial Mode Enable GPIO.

Same for this.

Thanks,
Conor.

> 
> > > I went over the device datasheets and I could not find the
> > > reason for the reset gpio. I left it there because it was being used
> > > in the current driver implementation, and I would not like to
> > > invalidate designs that might be currently using it. I will ask around.
> > 
> > If none of the devices have a reset pin, then you should delete the
> > property from the binding and the driver. Not like you're going to break
> > something if none of the supported devices even have the pin!
> 
> The pin might have been there due to an old revision of the ada4961 device
> (the reset_gpio was added to the code when ada4961 support was included)
> which I can't find related documentation. However, it turns out that
> hmc271a contains a reset pin, as you can see above.
> 
> -- 
> Kind regards,
> 
> Rodrigo Alencar

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