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

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Message-ID: <AM0PR04MB4481867284EAC2879DDD9F93881C0@AM0PR04MB4481.eurprd04.prod.outlook.com>
Date:   Fri, 7 Feb 2020 11:46:25 +0000
From:   Peng Fan <peng.fan@....com>
To:     Sudeep Holla <sudeep.holla@....com>, Marc Zyngier <maz@...nel.org>
CC:     "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 11:09:48AM +0000, Marc Zyngier wrote:
> > On 2020-02-07 11:00, Peng Fan wrote:
> > > > 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.
> > >
> > > ok. Then just like psci node,
> > > Add a "method" property for each protocol, and add "arm,func-id" to
> > > indicate the ID.
> > >
> > > How about this?
> >
> > Or rather just a function ID, full stop. the conduit *MUST* be
> > inherited from the PSCI context.
> 
> Absolutely, this is what I was expecting.
> 
> Peng,
> 
> You have already introduced a compatible for smc/hvc transport instead of
> default mailbox, why do you need anything more ? 

No.

Just use SMC or HVC
> conduit from PSCI/SMCCC. I don't think you need anything more than the
> function ID.

Yes, only function ID for now. If function ID could not be standardized in short
term, I could first mark smc-id optional in dt bindings, then smc transports
driver will first parse smc-id, abort if not exist. When ARM has standarlized
ID, we could switch to use that ID if smc-id not exist.

Thanks,
Peng.

> 
> --
> Regards,
> Sudeep