linux-kernel - Re: [RFC PATCH 0/1] dt-bindings: arm: Add scmi

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Message-ID: <20220301161034.GA78066@EPUAKYIW015D>
Date:   Tue, 1 Mar 2022 16:10:34 +0000
From:   Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
CC:     Sudeep Holla <sudeep.holla@....com>,
        Cristian Marussi <cristian.marussi@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Souvik Chakravarty <Souvik.Chakravarty@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/1] dt-bindings: arm: Add scmi_devid paramter for

Hi Stefano,

On Thu, Feb 24, 2022 at 02:51:42PM -0800, Stefano Stabellini wrote:
> On Thu, 24 Feb 2022, Sudeep Holla wrote:
> > On Tue, Feb 22, 2022 at 05:15:49PM +0000, Oleksii Moisieiev wrote:
> > > Hi Sudeep,
> > > 
> > > On Tue, Feb 22, 2022 at 04:06:37PM +0000, Sudeep Holla wrote:
> > > > Hi Oleksii,
> > > > 
> > > > My initial feedback on this. And thanks Cristian for making it so easy as
> > > > you have covered most of the things in depth(which I might have not done
> > > > myself that well)
> > > > 
> > > > On Tue, Feb 22, 2022 at 11:00:03AM +0000, Cristian Marussi wrote:
> > > > > On Mon, Feb 21, 2022 at 05:26:46PM +0000, Oleksii Moisieiev wrote:
> > > > > > Introducing new parameter called scmi_devid to the device-tree bindings.
> > > > > > This parameter should be set for the device nodes, which has
> > > > > > clocks/power-domains/resets working through SCMI.
> > > > 
> > > > I prefer you had given more details on your usage model here instead of
> > > > pointing to the other Xen thread as it helps for someone without much
> > > > background on Xen or your use-case to review this.
> > > > 
> > > Let me describe the process in few words:
> > > We implemented a new feature, called SCI-mediator in Xen.
> > > The proposed implementation allows Guests to communicate with the Firmware using SCMI
> > > protocol with SMC as a transport. Other implementation are also
> > > possible, such as SCMI-Mailbox, SCPI-mailbox etc.
> > > 
> > > In this feature Xen is the Trusted Agent, which receives the following
> > > information in Xen device-tree:
> > > 1) All channels should be described, each channel defined as
> > > arm,scmi-shmem node;
> > > 2) Scmi node arm,scmi-smc with protocols description;
> > 
> > Sounds good so far.
> > 
> > > 3) scmi-devid should be set in nodes, which works through SCMI.
> > >
> > 
> > Why is this needed for Guest OS, you need not populate this if Guest OS
> > is not required to use it, right ? If it is needed just by Xen hypervisor,
> > lets talk about that and why it is bad idea to mix that with general
> > SCMI bindings.
> 
> I'll try to help Oleksii by answering here, I hope I am not off the mark
> :-)

I appreciate it.

> 
> I think Sudeep is right, scmi-devid is not needed by the guest OS.
> 

I agree. I think this should be handled by Xen.

Best regards,
Oleksii.