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

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Message-ID: <20200207113235.GC40103@bogus>
Date:   Fri, 7 Feb 2020 11:32:35 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Peng Fan <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, dl-linux-imx <linux-imx@....com>,
        andre.przywara@....com, 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 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 ? Just
use SMC or HVC conduit from PSCI/SMCCC. I don't think you need anything
more than the function ID.

--
Regards,
Sudeep