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

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Message-ID: <ce775af0803d174fa2ad5dfc797592d9@kernel.org>
Date:   Fri, 07 Feb 2020 11:09:48 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Peng Fan <peng.fan@....com>
Cc:     Sudeep Holla <sudeep.holla@....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
Subject: Re: [PATCH 1/2] dt-bindings: arm: arm,scmi: add smc/hvc transports

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.

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