linux-kernel - Re: [PATCH v3 2/2] dt-bindings: hwmon: Add sample averaging properties for ADM1275

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Message-ID: <eb049c6f-f196-95de-265e-c3454fcb808a@roeck-us.net>
Date:   Mon, 28 Feb 2022 06:54:01 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Potin Lai <potin.lai@...ntatw.com>,
        Jean Delvare <jdelvare@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk@...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 v3 2/2] dt-bindings: hwmon: Add sample averaging
 properties for ADM1275

On 2/28/22 02:37, 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
> 
> Signed-off-by: Potin Lai <potin.lai@...ntatw.com>
> 
> doc
> ---
>   .../bindings/hwmon/adi,adm1275.yaml           | 39 +++++++++++++++++++
>   1 file changed, 39 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml b/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
> index 223393d7cafd..bc4206b257a8 100644
> --- a/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
> +++ b/Documentation/devicetree/bindings/hwmon/adi,adm1275.yaml
> @@ -37,6 +37,43 @@ 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
> +    minimum: 1
> +    maximum: 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.
> +

Both properties should only accept 1, 2, 4, 8, 16, 32, 64, and 128.

We accept non-exact numbers in sysfs attributes because we can not
expect the end users to know permitted values, but devicetree authors
should know what is acceptable. Valid values can be expressed here
easily with something like
	enum: [1, 2, 4, 8, 16, 32, 64, 128]

This can also be easily tested in the code by ensuring that
the devicetree property is in the range of 1..128 and has exactly
one bit set, such as
	if (!val || val > 128 || hweight32(val) != 1)
or with something like
	if (!val || val > 128 || BIT(__fls(val)) != val)

Guenter

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 1
> +    maximum: 128
> +    default: 1
> +
> +if:
> +  not:
> +    properties:
> +      compatible:
> +        contains:
> +          enum:
> +          - adi,adm1272
> +          - adi,adm1278
> +          - adi,adm1293
> +          - adi,adm1294
> +then:
> +  properties:
> +    adi,power-sample-average:
> +      description: This property is not allowed.
> +
>   required:
>     - compatible
>     - reg
> @@ -53,5 +90,7 @@ examples:
>               compatible = "adi,adm1272";
>               reg = <0x10>;
>               shunt-resistor-micro-ohms = <500>;
> +            adi,volt-curr-sample-average = <128>;
> +            adi,power-sample-average = <128>;
>           };
>       };