Re: [RFC][PATCH] dt-bindings: iio: accel: add adi,adxl345.yaml binding

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

On Mon, 2019-05-06 at 14:46 +0300, Alexandru Ardelean wrote:
> This patch adds a YAML binding for the Analog Devices ADXL345 I2C/SPI
> accelerometer.
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> ---
> 
> And now for the RFC part.
> Normally, I would dig into source-code to try to figure this out, but at
> this point-in-time, I am low on time/energy to do this.
> And maybe this helps trigger a discussion about this.
> 
> Apologies if this has been coverted on the devicetree mailing list, but
> at least we'd get some coverage on the IIO list (with this).
> 
> The ADXL345 device (as others) supports both I2C & SPI interfaces.
> 
> Question1: do we write 2 YAML files, or 1 ? I was looking at Zephyr (for
> some ideas/reference) but it seems to me that the YAML DT binding format
> is
> different than this one ? They write 2 files for ADXL372 (1 for SPI, 1
> for
> I2C).
> 
> Question1-a: one thing is that SPI requires some props to be `required`
> that would not be required for the I2C binding. This could be solved by
> doing 2 files, but if doing 1 YAML file, is there a way to do conditional
> `required` ? i.e. property is required if `SPI` ? not sure how to check
> for
> SPI vs I2C, it would be interesting (at some point) to somehow enforce
> SPI/I2C bindings correctness.
> 
> Question2: `make dt_binding_check` seems to generate only the first
> example. Is this known behavior, or do I need to take something else into
> consideration ?
> 
> Question3: one idea that was neat in Zephyr, is that there is a
> 'inherits'
> + `!include` mechanism for including common SPI & I2C device stuff. It
> would be neat to have this. Is there a way to do this now, or maybe this
> would come later ? Maybe, just having a way to include a YAML file into
> another would be interesting.
> 
>  .../bindings/iio/accel/adi,adxl345.yaml       | 63 +++++++++++++++++++
>  1 file changed, 63 insertions(+)
>  create mode 100644
> Documentation/devicetree/bindings/iio/accel/adi,adxl345.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/accel/adi,adxl345.yaml
> b/Documentation/devicetree/bindings/iio/accel/adi,adxl345.yaml
> new file mode 100644
> index 000000000000..246b90c07aaa
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/accel/adi,adxl345.yaml
> @@ -0,0 +1,63 @@
> +# SPDX-License-Identifier: GPL-2.0
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/accelerometers/adi,adxl345.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Analog Devices ADXL345/ADXL375 3-Axis Digital Accelerometers
> +
> +maintainers:
> +  - Michael Hennerich <michael.hennerich@analog.com>
> +
> +description: |
> +  Driver for Analog Devices ADXL345/ADXL375 3-Axis Digital
> Accelerometers
> +    http://www.analog.com/en/products/mems/accelerometers/adxl345.html
> +    
> http://www.analog.com/en/products/sensors-mems/accelerometers/adxl375.html
> +
> +properties:
> +  compatible:
> +    oneOf:
> +      - items:
> +          - enum:
> +              - adi,adxl345
> +              - adi,adxl375
> +
> +  reg:
> +    description:
> +      The I2C address or SPI chip select number of the sensor
> +    maxItems: 1
> +
> +  spi-cpha:
> +    description:
> +      SPI clock phase must be set, to select SPI mode 3
> +
> +  spi-cpol:
> +    description:
> +      SPI clock polarity must be set, to select SPI mode 3
> +
> +  interrupts:
> +    description:
> +      A variable number of interrupts warrants a description of what
> conditions
> +      affect the number of interrupts. Otherwise, descriptions on
> standard
> +      properties are not necessary.
> +

oops,
since i left this un-changed
oh, well, it's an RFC anyway :)
it would have received a V2 anyway

> +required:
> +  - compatible
> +  - reg
> +
> +examples:
> +  - |
> +    /* Example for a I2C device node */
> +    accelerometer@2a {
> +         compatible = "adi,adxl345";
> +         reg = <0x53>;
> +    };
> +  - |
> +    /* Example for a SPI device node */
> +    accelerometer@0 {
> +         compatible = "adi,adxl345";
> +         reg = <0>;
> +         spi-max-frequency = <5000000>;
> +         spi-cpol;
> +         spi-cpha;
> +    };