linux-kernel - Re: [PATCH 1/2] dt-bindings: firmware: arm,scmi: support parameter passing in smc/hvc

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Date:   Mon, 10 Apr 2023 19:20:25 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Nikunj Kela <quic_nkela@...cinc.com>, sudeep.holla@....com
Cc:     cristian.marussi@....com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: firmware: arm,scmi: support parameter
 passing in smc/hvc

On 09/04/2023 20:19, Nikunj Kela wrote:
> Currently, smc/hvc calls are made with smc-id only. The parameters are
> all set to zeros. This patch defines two optional device tree bindings,
> that can be used to pass parameters in smc/hvc calls.
> 
> This is useful when multiple scmi instances are used with common smc-id.
> 
> Signed-off-by: Nikunj Kela <quic_nkela@...cinc.com>
> ---
>  .../devicetree/bindings/firmware/arm,scmi.yaml   | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> index 5824c43e9893..08c331a79b80 100644
> --- a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> +++ b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> @@ -115,6 +115,22 @@ properties:
>      description:
>        SMC id required when using smc or hvc transports
>  
> +  arm,smc32-params:
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +    description:
> +      An optional parameter list passed in smc32 or hvc32 calls
> +    default: 0
> +    minItems: 1
> +    maxItems: 6
> +
> +  arm,smc64-params:
> +    $ref: /schemas/types.yaml#/definitions/uint64-array
> +    description:
> +      An optional parameter list passed in smc64 or hvc64 calls
> +    default: 0
> +    minItems: 1
> +    maxItems: 6

These do not look like hardware properties and the fact that you need
two properties for the same also points that you tied it to specific SW
interface.

Why this should be board-specific? Actually better question - why this
should be fixed per board? Doesn't my software want to have different
parameters, depending on some other condition?

You also did not provide any DTS user for this, so difficult to judge
usefulness.

Best regards,
Krzysztof