linux-kernel - Re: [PATCH v6 4/6] dt-bindings: iio: Add adis16550 bindings

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Message-ID: <20250205-styling-chirpy-79eae9437b3b@spud>
Date: Wed, 5 Feb 2025 19:52:37 +0000
From: Conor Dooley <conor@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>
Cc: Robert Budai <robert.budai@...log.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Alexandru Ardelean <alexandru.ardelean@...log.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jonathan Corbet <corbet@....net>, Nuno Sa <nuno.sa@...log.com>,
	Ramona Gradinariu <ramona.gradinariu@...log.com>,
	Trevor Gamblin <tgamblin@...libre.com>,
	Marcelo Schmitt <marcelo.schmitt@...log.com>,
	Paul Cercueil <paul@...pouillou.net>,
	David Lechner <dlechner@...libre.com>,
	Antoniu Miclaus <antoniu.miclaus@...log.com>,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 4/6] dt-bindings: iio: Add adis16550 bindings

On Wed, Feb 05, 2025 at 04:11:51PM +0000, Nuno Sá wrote:
> On Tue, 2025-02-04 at 19:25 +0000, Conor Dooley wrote:
> > On Tue, Feb 04, 2025 at 04:36:08PM +0200, Robert Budai wrote:
> > > Document the ADIS16550 device devicetree bindings.
> > > 
> > > Co-developed-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
> > > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
> > > Signed-off-by: Ramona Gradinariu <ramona.gradinariu@...log.com>
> > > Signed-off-by: Robert Budai <robert.budai@...log.com>
> > > ---
> > > 
> > > v6:
> > > - applied blank line suggestions
> > > - added clock-frequency dependency change suggestions
> > > - yamllint corrections
> > > 
> > >  .../bindings/iio/imu/adi,adis16550.yaml       | 83 +++++++++++++++++++
> > >  MAINTAINERS                                   |  9 ++
> > >  2 files changed, 92 insertions(+)
> > >  create mode 100644
> > > Documentation/devicetree/bindings/iio/imu/adi,adis16550.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/iio/imu/adi,adis16550.yaml
> > > b/Documentation/devicetree/bindings/iio/imu/adi,adis16550.yaml
> > > new file mode 100644
> > > index 000000000000..8750bb937979
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/iio/imu/adi,adis16550.yaml
> > > @@ -0,0 +1,83 @@
> > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/iio/imu/adi,adis16550.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Analog Devices ADIS16550 and similar IMUs
> > > +
> > > +maintainers:
> > > +  - Nuno Sa <nuno.sa@...log.com>
> > > +  - Ramona Gradinariu <ramona.gradinariu@...log.com>
> > > +  - Antoniu Miclaus <antoniu.miclaus@...log.com>
> > > +
> > > +properties:
> > > +  compatible:
> > > +    enum:
> > > +      - adi,adis16550
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  spi-cpha: true
> > > +  spi-cpol: true
> > > +
> > > +  spi-max-frequency:
> > > +    maximum: 15000000
> > > +
> > > +  vdd-supply: true
> > > +
> > > +  interrupts:
> > > +    maxItems: 1
> > > +
> > > +  reset-gpios:
> > > +    description:
> > > +      Must be the device tree identifier of the RESET pin. If specified,
> > > +      it will be asserted during driver probe. As the line is active low,
> > > +      it should be marked GPIO_ACTIVE_LOW.
> > > +    maxItems: 1
> > > +
> > > +  clocks:
> > > +    description: If not provided, then the internal clock is used.
> > > +    maxItems: 1
> > > +
> > > +  clock-frequency:
> > > +    description: Clock frequency in Hz when an external clock is used.
> > > +    oneOf:
> > > +      - minimum: 1
> > > +        maximum: 128
> > > +      - minimum: 3000
> > > +        maximum: 4500
> > 
> > I don't get why this is a property, to be honest. When you've got an
> > external clock, why isn't the frequency obtained from the clock provider
> > node?
> > 
> 
> The main purpose of this property is actually to show/document the constrains of
> the external clock. We can very well just error out in the driver (and we do
> that) and not have this property. I mentioned this property to Robert some
> revisions ago and I also pointed out that I wasn't really sure if it should be
> used or not (I guess this is more for fixed clock providers...). IIRC, I did
> asked for some advice/comments but we got none so I assume Robert just decided
> to use it and see what you guys had to say about it.

NGL, this is one of the kinda of things where if you're relying on
dt-bindings to avoid cocking up your board design, things have already
gotten pretty badly wrong! That said, "clock-frequency" is a
property for cpus, fixed-frequency clock providers and i2c buses, you'd
need a vendor prefix and a unit suffix here IMO. Also, I don't really
think that it actually does anything at all, given it does not constrain the
clock you're linking to with the clocks property. This may as well just be
a comment in the description of the clocks property, for all that it does.

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