linux-kernel - Re: [PATCH v3 1/2] dt-bindings: clock: fixed-clock: Add nvmem support

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Date:   Mon, 5 Jun 2023 15:38:13 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Mike Looijmans <mike.looijmans@...ic.nl>,
        devicetree@...r.kernel.org, linux-clk@...r.kernel.org
Cc:     Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] dt-bindings: clock: fixed-clock: Add nvmem support

On 05/06/2023 15:34, Mike Looijmans wrote:
> Add bindings for a fixed-rate clock that retrieves its rate from an
> NVMEM provider. This allows to store clock settings in EEPROM or EFUSE
> or similar device.
> 
> Component shortages lead to boards being shipped with different clock
> crystals, based on what was available at the time. The clock frequency
> was written to EEPROM at production time. Systems can adapt to a wide
> range of input frequencies using the clock framework, but this required
> us to patch the devicetree at runtime or use some custom driver. This
> provides a more generic solution.
> 
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> 
> ---
> 
> Changes in v3:
> Modify fixed-clock instead of introducing nvmem-clock
> 
> Changes in v2:
> Changed "fixed-clock" into "nvmem-clock" in dts example
> Add minItems:1 to nvmem-cell-names
> 
>  .../bindings/clock/fixed-clock.yaml           | 25 ++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/clock/fixed-clock.yaml b/Documentation/devicetree/bindings/clock/fixed-clock.yaml
> index b0a4fb8256e2..23e4df96d3b0 100644
> --- a/Documentation/devicetree/bindings/clock/fixed-clock.yaml
> +++ b/Documentation/devicetree/bindings/clock/fixed-clock.yaml
> @@ -12,7 +12,9 @@ maintainers:
>  
>  properties:
>    compatible:
> -    const: fixed-clock
> +    enum:
> +      - fixed-clock
> +      - fixed-clock-nvmem

Do you even need new compatible? Isn't this the same clock from the
hardware point of view?

>  
>    "#clock-cells":
>      const: 0
> @@ -33,6 +35,27 @@ required:
>  
>  additionalProperties: false
>  

Put it under allOf. Entire block should be before additionalProperties
(just like in example-schema).

> +if:
> +  properties:
> +    compatible:
> +      contains:
> +        const: fixed-clock-nvmem
> +
> +then:
> +  properties:
> +    nvmem-cells:
> +      maxItems: 2

Anyway, I don't think you tested it. Provide a DTS user of this. I don't
think it works and such user would point to mistakes.

Properties should be defined in top-level properties:, not in
allOf:if:then. In allOf:if:then you only narrow them.


> +      description:
> +        Reads clock-frequency and/or clock-accuracy from an NVMEM provider in
> +        binary native integer format. The size of the NVMEM cell can be 1, 2, 4
> +        or 8 bytes. If the contents of the nvmem are all zeroes or all 0xff, the
> +        value reverts to the one given in the property.
> +

Best regards,
Krzysztof