linux-kernel - Re: [PATCH 2/2] dt-bindings: iio: adc: nxp,imx93-adc.yaml: Add calibration properties

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Date: Fri, 22 Mar 2024 09:14:25 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Andrej Picej <andrej.picej@...ik.com>, haibo.chen@....com,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org
Cc: jic23@...nel.org, lars@...afoo.de, shawnguo@...nel.org,
 s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, robh@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 upstream@...ts.phytec.de
Subject: Re: [PATCH 2/2] dt-bindings: iio: adc: nxp,imx93-adc.yaml: Add
 calibration properties

On 22/03/2024 08:39, Andrej Picej wrote:
> On 20. 03. 24 13:15, Krzysztof Kozlowski wrote:
>> On 20/03/2024 13:05, Andrej Picej wrote:
>>> Hi Krzysztof,
>>>
>>> On 20. 03. 24 11:26, Krzysztof Kozlowski wrote:
>>>> On 20/03/2024 11:04, Andrej Picej wrote:
>>>>> Document calibration properties and how to set them.
>>>>
>>>> Bindings are before users.
>>>
>>> will change patch order when I send a v2.
>>>
>>>>
>>>> Please use subject prefixes matching the subsystem. You can get them for
>>>> example with `git log --oneline -- DIRECTORY_OR_FILE` on the directory
>>>> your patch is touching.
>>>> There is no file extension in prefixes.
>>>
>>> So: dt-bindings: iio/adc: nxp,imx93-adc: Add calibration properties?
>>
>> Did you run the command I proposed? I don't see much of "/", but except
>> that looks good.
> 
> Ok noted.
> 
>>
>>>
>>>>
>>>>>
>>>>> Signed-off-by: Andrej Picej <andrej.picej@...ik.com>
>>>>> ---
>>>>>    .../bindings/iio/adc/nxp,imx93-adc.yaml           | 15 +++++++++++++++
>>>>>    1 file changed, 15 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml b/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
>>>>> index dacc526dc695..64958be62a6a 100644
>>>>> --- a/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
>>>>> +++ b/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
>>>>> @@ -46,6 +46,21 @@ properties:
>>>>>      "#io-channel-cells":
>>>>>        const: 1
>>>>>    
>>>>> +  nxp,calib-avg-en:
>>>>> +    description:
>>>>> +      Enable or disable averaging of calibration time.
>>>>> +    enum: [ 0, 1 ]
>>>>> +
>>>>> +  nxp,calib-nr-samples:
>>>>> +    description:
>>>>> +      Selects the number of averaging samples to be used during calibration.
>>>>> +    enum: [ 16, 32, 128, 512 ]
>>>>> +
>>>>> +  nxp,calib-t-samples:
>>>>> +    description:
>>>>> +      Specifies the sample time of calibration conversions.
>>>>> +    enum: [ 8, 16, 22, 32 ]
>>>>
>>>> No, use existing, generic properties. Open other bindings for this.
>>>
>>> You mean I should use generic properties for the ADC calibration
>>> settings? Is there already something in place? Because as I understand
>>> it, these calib-* values only effect the calibration process of the ADC.
>>
>> Please take a look at other devices and dtschema. We already have some
>> properties for this... but maybe they cannot be used?
>>
> 
> I did look into other ADC devices, grep across iio/adc, adc bindings 
> folders and couldn't find anything closely related to what we are 
> looking for. Could you please point me to the properties that you think 
> should be used for this?

Indeed, there are few device specific like qcom,avg-samples. We have
though oversampling-ratio, settling-time-us and min-sample-time (which
is not that good because does not use unit suffix).

Then follow up questions:
 - nxp,calib-avg-en: Why is it a board-level decision? I would assume
this depends on user choice and what kind of input you have (which could
be board dependent or could be runtime decision).
 - nxp,calib-t-samples: what does it mean? Time is expressed in time
units, but there is nothing about units in the property name.

Best regards,
Krzysztof