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

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Message-ID: <455c737109271b0536617e179ffa2606@kernel.org>
Date:   Fri, 07 Feb 2020 11:01:58 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Peng Fan <peng.fan@....com>
Cc:     Sudeep Holla <sudeep.holla@....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, dl-linux-imx <linux-imx@....com>,
        andre.przywara@....com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] dt-bindings: arm: arm,scmi: add smc/hvc transports

On 2020-02-07 10:55, Peng Fan wrote:
>> 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.
> 
> The multiple protocols might use SMC or HVC. Saying
> 
>  Protocol@x {
>     method="smc";
>     arm,func-id=<0x....>
>  };
>  Protocol@y {
>     method="hvc";
>     arm,func-id=<0x....>
>  };
> 
> With my propose:
> 
> Protocol@x {
>     arm,smc-id=<0x....>
>  };
>  Protocol@y {
>     arm,hvc-id=<0x....>
>  };
> 
> No need an extra method property to indicate it is smc or hvc.
> The driver use take arm,smc-id as SMC, arm,hvc-id as HVC.

You're missing the point. I do not want to see different IDs depending 
on
Whether we use HVC and SMC. They *MUST* have the same value, and the 
right
way to enforce this is to disallow any indication of the conduit.

An even better thing would be for ARM to mandate the ID, so that vendors
can be deprived of their special "value add" once and for all.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...