RE: [PATCH v4 4/6] dt-bindings: iio: Add adis16550 bindings

["Budai, Robert" <Robert.Budai@analog.com>]

> -----Original Message-----
> From: Nuno Sá <noname.nuno@gmail.com>
> Sent: Monday, January 13, 2025 11:30 AM
> To: Jonathan Cameron <jic23@kernel.org>; Budai, Robert
> <Robert.Budai@analog.com>
> Cc: Sa, Nuno <Nuno.Sa@analog.com>; Gradinariu, Ramona
> <Ramona.Gradinariu@analog.com>; Miclaus, Antoniu
> <Antoniu.Miclaus@analog.com>; Lars-Peter Clausen <lars@metafoo.de>;
> Hennerich, Michael <Michael.Hennerich@analog.com>; Rob Herring
> <robh@kernel.org>; Krzysztof Kozlowski <krzk+dt@kernel.org>; Conor Dooley
> <conor+dt@kernel.org>; Jonathan Corbet <corbet@lwn.net>; Alex Lanzano
> <lanzano.alex@gmail.com>; linux-iio@vger.kernel.org;
> devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-
> doc@vger.kernel.org
> Subject: Re: [PATCH v4 4/6] dt-bindings: iio: Add adis16550 bindings
> 
> [External]
> 
> On Sun, 2025-01-12 at 15:48 +0000, Jonathan Cameron wrote:
> > On Fri, 10 Jan 2025 09:42:52 +0200
> > Robert Budai <robert.budai@analog.com> wrote:
> >
> > > Document the ADIS16550 device devicetree bindings.
> > >
> > > Co-developed-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
> > > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
> > > Signed-off-by: Ramona Gradinariu <ramona.gradinariu@analog.com>
> > > Signed-off-by: Robert Budai <robert.budai@analog.com>
> > > ---
> > >
> > > 4:
> > > - applied styling changes to the bindings file
> > > - restricted sync-mode to intervals 1-2
> > >
> > >  .../bindings/iio/imu/adi,adis16550.yaml       | 96 +++++++++++++++++++
> > >  MAINTAINERS                                   |  9 ++
> > >  2 files changed, 105 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..e7ccf3883e55
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/iio/imu/adi,adis16550.yaml
> > > @@ -0,0 +1,96 @@
> > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id:
> https://urldefense.com/v3/__http://devicetree.org/schemas/iio/imu/adi,adis
> 16550.yaml*__;Iw!!A3Ni8CS0y2Y!74KHajr7iKZQ7Ld5deb4LytVFckO_Og8tIG
> Ukf233OLregM6AqtN-v-IBRfAn-4Z1tC0bwbcEpNO7Glv8YjiXWI$
> > > +$schema: https://urldefense.com/v3/__http://devicetree.org/meta-
> schemas/core.yaml*__;Iw!!A3Ni8CS0y2Y!74KHajr7iKZQ7Ld5deb4LytVFckO_
> Og8tIGUkf233OLregM6AqtN-v-IBRfAn-4Z1tC0bwbcEpNO7GlvNAV5ERI$
> > > +
> > > +title: Analog Devices ADIS16550 and similar IMUs
> > > +
> > > +maintainers:
> > > +  - Nuno Sa <nuno.sa@analog.com>
> > > +  - Ramona Gradinariu <ramona.gradinariu@analog.com>
> > > +  - Antoniu Miclaus <antoniu.miclaus@analog.com>
> > > +
> > > +properties:
> > > +  compatible:
> > > +    enum:
> > > +      - adi,adis16550
> > > +      - adi,adis16550w
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  spi-cpha: true
> > > +
> > > +  spi-cpol: true
> > > +
> > > +  spi-max-frequency:
> > > +    maximum: 15000000
> > > +
> > > +  vdd-supply: true
> > > +
> > > +  interrupts:
> > > +    maxItems: 1
> > > +
> > > +  reset-gpios:
> > > +    description:
> > > +      RESET active low pin.
> > > +    maxItems: 1
> > > +
> > > +  clocks:
> > > +    maxItems: 1
> > > +    description: If not provided, then the internal clock is used.
> > > +
> > > +  adi,sync-mode:
> > > +    description:
> > > +      Configures the device SYNC pin. The following modes are supported
> > > +      0 - output_sync
> > > +      1 - direct_sync
> > > +      2 - scaled_sync
> >
> > A little more on these would be good.  They are 'weird' options
> > that are not commonly seen so help the reader out.
> >
> > For scaled_sync don't we need information on the scale for it to be useful?
> > If we had that then a value of 1 would mean direct sync and wouldn't need
> > another control.
> >
> > I'm not fully understanding the usecases for this.
> >
> > If we have a say a pulse per second input, the control of the scale should
> > be userspace anyway.  So maybe this maps to the input clock that we can
> elect
> > to
> > use and control the effective frequency of by using scaled sync?
> 
> I guess you likely already saw it in the driver. The scale value is
> automatically set by the driver depending on the desired ODR (sampling
> frequency).
> 
> >
> > I'm not sure what pulse sync is. Grepping the datasheet didn't give me
> > anything that seemed related.   The sync pin is input only so I'm also
> > not sure on output sync.
> 
> I think this is a copy paste from the adis16475 bindings. For this device, it
> seems we only have:
>  * internal clock;
>  * external:
>    * direct mode
>    * scaled mode
> 
> But yeah, as you pointed out I think we do not need the binding. The presence
> of
> an optional input clock plus the frequency should be all we need in order to set
> the desired configuration. It should also be possible to add the allowed ranges
> to the external input clock in the bindings...
> 
> 
> - Nuno Sá
> 
Will drop this binding than and add a frequency one that is dependent on clock 
with specified ranges.

- Robert Budai