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Message-ID: <b68807e9-3907-9f9a-8eee-b7f24be3c78f@sholland.org>
Date:   Sun, 27 Nov 2022 12:01:30 -0600
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To:     Jonathan Cameron <jic23@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc:     Lars-Peter Clausen <lars@metafoo.de>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        devicetree@vger.kernel.org, linux-iio@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20221125220903.8632-1-samuel@sholland.org>
 <e4be94a3-cdfc-cdf8-5d69-0eef480033f9@linaro.org>
 <20221127174219.34d0406c@jic23-huawei>
From:   Samuel Holland <samuel@sholland.org>
Subject: Re: [PATCH] dt-bindings: iio: adc: ti,adc081c: Document the binding
In-Reply-To: <20221127174219.34d0406c@jic23-huawei>
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On 11/27/22 11:42, Jonathan Cameron wrote:
> On Sun, 27 Nov 2022 13:51:19 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> wrote:
> 
>> On 25/11/2022 23:09, Samuel Holland wrote:
>>> Linux has a driver for these ADCs at drivers/iio/adc/ti-adc081c.c, but
>>> the compatible strings were undocumented. Add a binding for them. The
>>> hardware has an alert interrupt output, but existing ti,adc081c users
>>> do not provide the 'interrupts' property, so leave it as optional.
>>>
>>> Signed-off-by: Samuel Holland <samuel@sholland.org>
>>> ---
>>>
>>>  .../bindings/iio/adc/ti,adc081c.yaml          | 55 +++++++++++++++++++
>>>  1 file changed, 55 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,adc081c.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,adc081c.yaml b/Documentation/devicetree/bindings/iio/adc/ti,adc081c.yaml
>>> new file mode 100644
>>> index 000000000000..caaad777580c
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/iio/adc/ti,adc081c.yaml
>>> @@ -0,0 +1,55 @@
>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/iio/adc/ti,adc081c.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: TI Single-channel I2C ADCs
>>> +
>>> +maintainers:
>>> +  - Jonathan Cameron <jic23@kernel.org>
>>> +  - Lars-Peter Clausen <lars@metafoo.de>
>>> +
>>> +description: |
>>> +  Single-channel ADC supporting 8, 10, or 12-bit samples and high/low alerts.
>>> +
>>> +properties:
>>> +  compatible:
>>> +    enum:
>>> +      - ti,adc081c
>>> +      - ti,adc101c
>>> +      - ti,adc121c
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>> +  vref-supply:
>>> +    description:
>>> +      Regulator for the combined power supply and voltage reference
>>> +
>>> +  "#io-channel-cells":
>>> +    const: 1
>>> +
>>> +required:
>>> +  - compatible
>>> +  - reg  
>>
>> Why not requiring io-channel-cells? If it is an IIO ADC provider, you
>> need the cells, right?
> 
> Only if anyone is using it as a provider.  If it's purely being used via
> IIO then there are no consumers registered.
> 
> So historically I've left it up to those defining the binding to decide if
> they think #io-channel-cells should be required or optional.
> 
> It gets a bit non obvious with some of the more complex special ADCs on whether
> they will ever be consumed.  This one is generic, so quite likely it will be.

I kept #io-channel-cells optional because there are already a handful of
boards using ti,adc081c without it.

On the board I am adding (Clockwork DevTerm), the ADC is used a
temperature sensor for a thermal printer. So whether or not the ADC is
used as an OF provider depends on how the printer driver gets implemented.

Regards,
Samuel