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

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Date:   Fri, 7 Feb 2020 11:06:02 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Peng Fan <peng.fan@....com>
Cc:     Marc Zyngier <maz@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "andre.przywara@....com" <andre.przywara@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <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 10:55:44AM +0000, 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....>
>  };
>

Wow, stop there. Please don't do that. You either use SMC or HVC consistently.
Not both at the same time. Any particular reasons for trying such crazy things.

> 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.
>

NACK, just have one function ID, I am not very particular on the name
'smc-id' is just fine for me. But only one function ID for any conduit
used and that is chosen by PSCI/SMCCC.

If you need multiple channels(unique per protocol) then I suggest go for
an channel ID or you can even manage just with shmem associated with it
(I prefer latter but again I am fine either way)

--
Regards,
Sudeep