linux-kernel - Re: [PATCH v2 2/2] dt-bindings: hwmon: Add sample averaging property for ADM1275

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Date:   Fri, 25 Feb 2022 09:56:04 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>,
        Potin Lai <potin.lai@...ntatw.com>,
        Jean Delvare <jdelvare@...e.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Patrick Williams <patrick@...cx.xyz>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 2/2] dt-bindings: hwmon: Add sample averaging property
 for ADM1275

On 25/02/2022 09:41, Guenter Roeck wrote:
> On 2/24/22 23:31, Krzysztof Kozlowski wrote:
>> On 25/02/2022 08:06, Krzysztof Kozlowski wrote:
>>> On 24/02/2022 16:43, Potin Lai wrote:
>>>> Add new properties for binding sample averaging in PMON_CONFIG register
>>>>
>>>> - adi,volt-curr-sample-average
>>>> - adi,power-sample-average
>>>>
>>>> Signed-off-by: Potin Lai <potin.lai@...ntatw.com>
>>>> ---
>>>>   .../bindings/hwmon/adi,adm1275.yaml           | 44 +++++++++++++++++++
>>>>   1 file changed, 44 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml b/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
>>>> index 223393d7cafd..325f6827648f 100644
>>>> --- a/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
>>>> +++ b/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
>>>> @@ -37,6 +37,48 @@ properties:
>>>>       description:
>>>>         Shunt resistor value in micro-Ohm.
>>>>   
>>>> +  adi,volt-curr-sample-average:
>>>> +    description: |
>>>> +      A value to configure VI_AVG in PMON_CONFIG register to indicate a
>>>> +      number of samples to be used to report voltage and currentvalues.
>>>
>>> missing space after current.
>>>
>>>> +      If set to 7, the 128 samples averaging would be used.
>>>> +
>>>> +    $ref: /schemas/types.yaml#/definitions/uint8
>>>
>>> Make it a uint32.
>>>
>>> The previous usage of this field was more appropriate. Instead of
>>> keeping register values in DT, it's better to keep logical value. What
>>> if in next cheap the register values have calculation method?
>>>
>>> This should be like in v1 - enum for number of samples to take in averaging.
>>>
>>
>> One more thought: this field could also stay in current approach if you
>> change the meaning from "value to configure VI_AVG" to something like
>> "the exponent used to determine the number of samples, where the base is 2".
>>
>> This approach would allow you to skip the "ilog" in the code. It sill
>> won't be that easily scalable if another chip comes with different
>> formula, but I think that's unlikely.
>>
> 
> The standard hwmon ABI expects the number of samples, it isn't always a
> power of 2, and the driver already implements it (with ilog2) as sysfs
> attribute. I don't really see the point of "optimizing" something
> like this to be chip specific just to avoid some error checking.

Thanks for confirming. +1



Best regards,
Krzysztof