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From:   Oleksii Moisieiev <Oleksii_Moisieiev@epam.com>
To:     "robh+dt@kernel.org" <robh+dt@kernel.org>
CC:     Oleksii Moisieiev <Oleksii_Moisieiev@epam.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
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        Stefano Stabellini <sstabellini@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: [RFC PATCH 0/1] dt-bindings: arm: Add scmi_devid paramter for
Thread-Topic: [RFC PATCH 0/1] dt-bindings: arm: Add scmi_devid paramter for
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Date:   Mon, 21 Feb 2022 17:26:46 +0000
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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@e6590000
{
    scmi_devid =3D <19>;
    clocks =3D <&scmi_clock 3>, <&scmi_clock 2>;
    resets =3D <&scmi_reset 10>, <&scmi_reset 9>;
    power-domains =3D <&scmi_power 0>;
};

Given example shows the configuration of the hsusb node, which is using
scmi to contol clocks, resets and power-domains. scmi_devid is set
equals to 19, which should match defined id for usb in the Firmware.

Trusted agent will use scmi_devid to set the device permissions for
the Agents. Guest OS should not have an access to the permissions
settings, so no code to process scmi_devid was presented in Linux
kernel.

We are currently contributing changes to Xen, which are intended to
mediate SCMI access from Guests to the Firmware. Xen uses scmi_devid to set
the permissions for the devices. See [1] thread for details.

[0] https://developer.arm.com/documentation/den0056/latest
[1] https://xen.markmail.org/message/mmi4fpb4qr6e3kad

---
Posting this patch as RFC because I'm not sure if I set maintainers
correctly. Hope community will help me so I could set the maintainers in
v2.

Oleksii Moisieiev (1):
  dt-bindings: arm: Add scmi_devid property description for SCMI

 .../bindings/firmware/arm,scmi-devid.yaml     | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/firmware/arm,scmi-dev=
id.yaml

--=20
2.27.0