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

[Nikunj Kela]

On 4/10/2023 10:20 AM, Krzysztof Kozlowski wrote:
> 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@xxxxxxxxxxx>
> > ---
> >   .../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.

This is certainly not the H/W property but then smc-id is also not H/W 
property either

but that gets passed via DTB. I could use the same property for both 
however I wasn't sure

which datatype should be used, uint32-array/uint64-array. Moreover, I 
thought if users are

passing parameters, they better know which SMC convention they are using 
hence used two

explicit properties.

> 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?

Not sure I follow, I didn't say this is board specific. People can use 
the parameters to pass

whatever their S/W demands. SMC/HVC calls are made by passing parameters 
which is what this patch is enabling.

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

The work is still on going and we will push the dts in few months, 
however that shouldn't stop

making changes in advance.

> Best regards,
> Krzysztof