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

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Date:   Tue, 22 Feb 2022 17:34:59 +0000
From:   Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     Krzysztof Kozlowski <krzk@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Cristian Marussi <cristian.marussi@....com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/1] dt-bindings: arm: Add scmi_devid paramter for

On Tue, Feb 22, 2022 at 04:14:40PM +0000, Sudeep Holla wrote:
> On Tue, Feb 22, 2022 at 09:06:25AM +0100, Krzysztof Kozlowski wrote:
> > On 21/02/2022 22:39, Oleksii Moisieiev wrote:
> > > Hi Krzysztof,
> > > 
> > > On Mon, Feb 21, 2022 at 10:01:43PM +0100, Krzysztof Kozlowski wrote:
> > >> On 21/02/2022 18:26, 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.
> > >>> Given parameter should set the device_id, needed to set device
> > >>> permissions in the Firmware. This feature will be extremely useful for
> > >>> the virtualized systems, which has more that one Guests running on the
> > >>> system at the same time or for the syestems, which require several
> > >>> agents with different permissions. Trusted agent will use scmi_devid to
> > >>> set the Device permissions for the Firmware (See Section 4.2.2.10 [0]
> > >>> for details).
> > >>> Agents concept is described in Section 4.2.1 [0].
> > >>>
> > >>> scmi_devid in Device-tree node example:
> > >>> usb@...90000
> > >>> {
> > >>>     scmi_devid = <19>;
> > >>>     clocks = <&scmi_clock 3>, <&scmi_clock 2>;
> > >>>     resets = <&scmi_reset 10>, <&scmi_reset 9>;
> > >>>     power-domains = <&scmi_power 0>;
> > >>> };
> > >>
> > >> And how do you prevent DT overlay adding such devid to any other node
> > >> thus allowing any other device to send requests with given devid?
> > >>
> > > Thank you for the quick response.
> > > scmi_devid value will be used only by Trusted Agent when the device
> > > permissions are set. Non-trusted agents, which in our case are
> > > represented as Guest OS are using scmi drivers, already present in linux
> > > kernel, ignores scmi_devid and uses scmi_clocks, scmi_power, scmi_reset
> > > nodes to access to SCMI protocol.
> > 
> > Ah, ok.
> > 
> > > 
> > >> Plus few technicalities:
> > >> 1. Hyphen, not underscore in property name, so scmi-devid.
> > > 
> > > Thanks for the tip, I will change that in v2.
> > 
> > Few more thoughts:
> > 1. This looks specific to ARM SCMI, so you also need vendor prefix, so
> > something like:
> > arm,scmi-devid
> > arm,scmi-device-id
> > 
> 
> Keeping the other discussion separate, I wanted to comment on this.
> I agree with Krzysztof on having vendor specific prefix if we decide to add
> this device id thing. However, I prefer not to use "arm,scmi-" here.
> It can be "xen,scmi-" as we had plans to introduce some concepts in SCMI
> spec that may use looks like this device-id. I would just like to avoid
> conflicting with that in the future. It may happen to be same in the future
> (i.e. this xen device-id matches 100% with definition of device-id we might
> introduce in the spec, but I want to make assumption otherwise and leave
> scope for divergence however small/little it can be). No issues even if
> they converge and match 100% later in the far future.
> 

xem,scmi- works for me. What do other thinks?