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

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Message-ID: <AM0PR04MB4481B84BF243926462EAF74B881C0@AM0PR04MB4481.eurprd04.prod.outlook.com>
Date:   Fri, 7 Feb 2020 11:19:22 +0000
From:   Peng Fan <peng.fan@....com>
To:     Sudeep Holla <sudeep.holla@....com>, Marc Zyngier <maz@...nel.org>
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>
Subject: RE: [PATCH 1/2] dt-bindings: arm: arm,scmi: add smc/hvc transports

> 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)

Ok. Just follow Marc suggested
Parse the conduit from PSCI context. Then only add 'smc-id' property in scmi
node, and take protocol reg as arg1. Is this ok for you?

Thanks,
Peng.

> 
> --
> Regards,
> Sudeep