linux-kernel - Re: [PATCH 1/2] dt-bindings: arm: arm,scmi: add smc/hvc transports

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Date:   Fri, 7 Feb 2020 10:47:36 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     peng.fan@....com, robh+dt@...nel.org, mark.rutland@....com,
        devicetree@...r.kernel.org, f.fainelli@...il.com,
        viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
        linux-imx@....com, andre.przywara@....com,
        linux-arm-kernel@...ts.infradead.org,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH 1/2] dt-bindings: arm: arm,scmi: add smc/hvc transports

On Fri, Feb 07, 2020 at 10:08:36AM +0000, Marc Zyngier wrote:
> On 2020-02-06 13:01, peng.fan@....com wrote:
> > From: Peng Fan <peng.fan@....com>
> >
> > SCMI could use SMC/HVC as tranports, so add into devicetree
> > binding doc.
> >
> > Signed-off-by: Peng Fan <peng.fan@....com>
> > ---
> >  Documentation/devicetree/bindings/arm/arm,scmi.txt | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/devicetree/bindings/arm/arm,scmi.txt
> > b/Documentation/devicetree/bindings/arm/arm,scmi.txt
> > index f493d69e6194..03cff8b55a93 100644
> > --- a/Documentation/devicetree/bindings/arm/arm,scmi.txt
> > +++ b/Documentation/devicetree/bindings/arm/arm,scmi.txt
> > @@ -14,7 +14,7 @@ Required properties:
> >
> >  The scmi node with the following properties shall be under the
> > /firmware/ node.
> >
> > -- compatible : shall be "arm,scmi"
> > +- compatible : shall be "arm,scmi" or "arm,scmi-smc"
> >  - mboxes: List of phandle and mailbox channel specifiers. It should
> > contain
> >  	  exactly one or two mailboxes, one for transmitting messages("tx")
> >  	  and another optional for receiving the notifications("rx") if
> > @@ -25,6 +25,8 @@ The scmi node with the following properties shall be
> > under the /firmware/ node.
> >  	  protocol identifier for a given sub-node.
> >  - #size-cells : should be '0' as 'reg' property doesn't have any size
> >  	  associated with it.
> > +- arm,smc-id : SMC id required when using smc transports
> > +- arm,hvc-id : HVC id required when using hvc transports
> >
> >  Optional properties:
>
> Not directly related to DT: Why do we need to distinguish between SMC and
> HVC?

IIUC you want just one property to get the function ID ? Does that align
with what you are saying ? I wanted to ask the same question and I see
no need for 2 different properties.

> Other SMC/HVC capable protocols are able to pick the right one based on the
> PSCI conduit.
>

This make it clear, but I am asking to  be sure.

> This is how the Spectre mitigations work already. Why is that any different?
>

I don't see any need for it to be different.

--
Regards,
Sudeep