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

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Message-ID: <178594a2-cd5f-4608-aae6-7d68fd0817e0@linaro.org>
Date: Mon, 25 Mar 2024 10:58:51 +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 10:58, Andrej Picej wrote:
> On 22. 03. 24 09:14, Krzysztof Kozlowski wrote:
>> 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).
> 
> Ok, these are examples but I think I should not use them, since these 
> are i.MX93 ADC specific settings, which are used for configuration of 


No vendor prefix, so they rather should be generic, not imx93
specific... But this the binding for imx93, so I don't understand your
statement.

> calibration process, and are not related to the standard conversion 
> process during runtime. Calibration process is the first step that 
> should be done after every power-on reset.
> 
>>
>> 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).
> 
> Not really sure I get your question, so please elaborate if I missed the 
> point.
> This is a user choice, to enable or disable the averaging function in 
> calibration, but this is a board-level decision, probably relates on 
> external ADC regulators and input connections. The same options are used 
> for every ADC channel and this can not be a runtime decision, since 
> calibration is done before the ADC is even registered.

You now mix how Linux driver behaves with hardware. Why you cannot
recalibrate later, e.g. when something else is being connected to the
exposed pins?

Best regards,
Krzysztof