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

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Date:   Fri, 07 Feb 2020 10:55:21 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
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
Subject: Re: [PATCH 1/2] dt-bindings: arm: arm,scmi: add smc/hvc transports

On 2020-02-07 10:47, Sudeep Holla wrote:
> 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.

Exactly. Using SMC or HVC should come from the context, and there is 
zero
value in having different different IDs, depending on the conduit.

We *really* want SMC and HVC to behave the same way. Any attempt to make
them different should just be NAKed.

Thanks,

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