linux-kernel - Re: [PATCH v4 2/2] dt-bindings: hwmon: Add sample averaging properties for ADM1275

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Message-ID: <39415d57-ec14-aab8-20fd-92d2a810f3fd@roeck-us.net>
Date:   Tue, 1 Mar 2022 08:47:11 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        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 v4 2/2] dt-bindings: hwmon: Add sample averaging
 properties for ADM1275

On 3/1/22 05:21, Krzysztof Kozlowski wrote:
> On 01/03/2022 13:42, POTIN LAI wrote:
>>
>> Krzysztof Kozlowski 於 1/03/2022 7:16 pm 寫道:
>>> On 01/03/2022 11:39, Potin Lai wrote:
>>>> Add documentation of new properties for sample averaging in PMON_CONFIG
>>>> register.
>>>>
>>>> New properties:
>>>> - adi,volt-curr-sample-average
>>>> - adi,power-sample-average
>>>> - adi,power-sample-average-enable
>>>>
>>>> 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..1b612dc06992 100644
>>>> --- a/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
>>>> +++ b/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
>>>> @@ -37,6 +37,47 @@ properties:
>>>>       description:
>>>>         Shunt resistor value in micro-Ohm.
>>>>   
>>>> +  adi,volt-curr-sample-average:
>>>> +    description: |
>>>> +      Number of samples to be used to report voltage and current values.
>>>> +      If the configured value is not a power of 2, sample averaging number
>>>> +      will be configured with smaller and closest power of 2.
>>>> +
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>> +    enum: [1, 2, 4, 8, 16, 32, 64, 128]
>>>> +    default: 1
>>>> +
>>>> +  adi,power-sample-average:
>>>> +    description: |
>>>> +      Number of samples to be used to report power values.
>>>> +      If the configured value is not a power of 2, sample averaging number
>>>> +      will be configured with smaller and closest power of 2.
>>>> +
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>> +    enum: [1, 2, 4, 8, 16, 32, 64, 128]
>>>> +    default: 1
>>>> +
>>>> +  adi,power-sample-average-enable:
>>>> +    description: Enable sample averaging for power reading.
>>>> +    type: boolean
>>> Why do you need this property? Voltage/current sampling is enabled in
>>> your driver with presence of adi,volt-curr-sample-average. Why power
>>> sampling is different?
>> For "adi,power-sample-average", adm1075, adm1275 & adm127 don't have config reg for power sample average, so I add boolean type property to enable it
>> But for "adi,power-sample-average-enable", all chips have ability of configuring, so it doesn't need a property to enable or disable.
> 
> So the reason to add separate property is that this feature can be
> disabled. Since your driver does not disable it, it seems it is a
> default state to have it disabled and you have to enable it, right?
> Where is the enable code? I see you only write the sample averaging
> value with adm1275_write_pmon_config(). There is no enable...
> 
> But wait, the power averaging is being disabled by writing 0 to
> register, which is not allowed by bindings. How one can disable it?
> 

Valid register values are 0..7, matching dt property values of
BIT(x) or 1 .. 128. Setting the property value to 1 (= 1 sample)
is equivalent to disabling sampling.

> I don't see any usage of "adi,power-sample-average-enable", neither in
> driver nor in hardware. I also do not see the need for it, the purpose.
> 
> Then second part, you added default value of 1 to
> adi,volt-curr-sample-average and adi,power-sample-average. If the
> property is missing, then the default of 1 is applied, right? But
> datasheet says that default is 128!
> 
> The bindings neither match hardware nor driver. They look entirely
> independent. This is wrong. They should instead be strongly related to
> the hardware, describe the hardware. Then the driver should implement
> proper logic for it.
> 

Agreed.

Guenter