linux-kernel - Re: [PATCH 1/2] add binding for iio adc driver for TI ADS1018

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Date:   Sat, 13 Nov 2021 18:09:16 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Iain Hunter <drhunter95@...il.com>
Cc:     Daniel Baluta <daniel.baluta@....com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] add binding for iio adc driver for TI ADS1018

On Tue, 9 Nov 2021 10:00:14 +0000
Iain Hunter <drhunter95@...il.com> wrote:

> Hi Daniel,
> I'm happy to add myself. I assume that is just a case of re-submitting the
> patch with my name instead of yours. Is that correct?

That would be perfect.  Thanks for taking this on,

A few comments below from me.

Jonathan

> Iain
> 
> On Mon, Nov 8, 2021 at 6:45 PM Daniel Baluta <daniel.baluta@....com> wrote:
> 
> > This looks good to me with the only mention that I don't actually have
> > time to maintain this :(.
> >
> > Perhaps you can add yourself?
> >
> > On 11/8/21 8:43 PM, Iain Hunter wrote:  
> > > Add a new binding for new IIO ADS1018 driver.
> > >
> > > Signed-off-by: Iain Hunter <drhunter95@...il.com>
> > > ---
> > >   .../bindings/iio/adc/ti,ads1018.yaml          | 109 ++++++++++++++++++
> > >   1 file changed, 109 insertions(+)
> > >   create mode 100644  
> > Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml  
> > >
> > > diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml  
> > b/Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml  
> > > new file mode 100644
> > > index 000000000000..ba0fdfba2c45
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml
> > > @@ -0,0 +1,109 @@
> > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/iio/adc/ti,ads1018.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: TI ADS1018 4 channel SPI analog to digital converter
> > > +
> > > +maintainers:
> > > +  - Daniel Baluta <daniel.baluta@....com>
> > > +
> > > +description: |
> > > +  Datasheet at: https://www.ti.com/lit/gpn/ads1018
> > > +  Supports both single ended and differential channels.
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: ti,ads1018
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  "#address-cells":
> > > +    const: 1
> > > +
> > > +  "#size-cells":
> > > +    const: 0
> > > +
> > > +  "#io-channel-cells":
> > > +    const: 1
> > > +
> > > +required:
> > > +  - compatible
> > > +  - reg
> > > +  - "#address-cells"
> > > +  - "#size-cells"
> > > +
> > > +additionalProperties: false
> > > +
> > > +patternProperties:
> > > +  "^channel@[0-7]+$":
> > > +    type: object
> > > +    description:
> > > +      Child nodes needed for each channel that the platform uses.
> > > +
> > > +    properties:
> > > +      reg:
> > > +        description: |
> > > +          0: Voltage over AIN0 and AIN1.
> > > +          1: Voltage over AIN0 and AIN3.
> > > +          2: Voltage over AIN1 and AIN3.
> > > +          3: Voltage over AIN2 and AIN3.
> > > +          4: Voltage over AIN0 and GND.
> > > +          5: Voltage over AIN1 and GND.
> > > +          6: Voltage over AIN2 and GND.
> > > +          7: Voltage over AIN3 and GND.

This should map to the generic channel description in
adc.yaml.  If we need to extend that then we can do that rather than a
separate device specific definition.

Note that is relatively new, so there are lots of drivers with older
bindings in tree that do things more closely to what you have here.


> > > +        items:
> > > +          - minimum: 0
> > > +            maximum: 7
> > > +
> > > +      ti,gain:
> > > +        $ref: /schemas/types.yaml#/definitions/uint32
> > > +        minimum: 0
> > > +        maximum: 5
> > > +        description: |
> > > +          pga is the programmable gain amplifier (values are full scale)
> > > +          0: +/- 6.144 V
> > > +          1: +/- 4.096 V
> > > +          2: +/- 2.048 V (default)
> > > +          3: +/- 1.024 V
> > > +          4: +/- 0.512 V
> > > +          5: +/- 0.256 V

Why a DT property? Normally we'd leave this to userspace control.

> > > +
> > > +      ti,datarate:
> > > +        $ref: /schemas/types.yaml#/definitions/uint32
> > > +        minimum: 0
> > > +        maximum: 6
> > > +        description: |
> > > +          Data acquisition rate in samples per second

Why is this a DT property?

If we do keep it as such use the actual values (via an enum)
and rename it to add -hz which will then remove the nee for the
$ref

> > > +          0: 128
> > > +          1: 250
> > > +          2: 490
> > > +          3: 920
> > > +          4: 1600 (default)
> > > +          5: 2400
> > > +          6: 3300
> > > +
> > > +    required:
> > > +      - reg
> > > +
> > > +examples:
> > > +  - |
> > > +    spi {
> > > +        #address-cells = <1>;
> > > +        #size-cells = <0>;
> > > +
> > > +        adc@1 {
> > > +            compatible = "ti,ads1018";
> > > +            reg = <0x1>;
> > > +            #address-cells = <1>;
> > > +            #size-cells = <0>;
> > > +            channel@4 {
> > > +              reg = <4>;
> > > +              ti,gain = <3>;
> > > +              ti,datarate = <5>;
> > > +            };
> > > +        };
> > > +    };
> > > +...  
> >