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

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Message-ID: <20260127-goes-grandpa-891eb0dc413a@spud>
Date: Tue, 27 Jan 2026 19:38:37 +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 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.

> 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!

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