linux-kernel - [PATCH v2 0/2] dt-bindings: xen: Add xen,scmi-devid parameter for

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Date:   Mon, 7 Mar 2022 08:17:43 +0000
From:   Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>
To:     "robh+dt@...nel.org" <robh+dt@...nel.org>
CC:     Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Cristian Marussi <cristian.marussi@....com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 0/2] dt-bindings: xen: Add xen,scmi-devid parameter for

Introducing new parameter called xen,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 property is used by Xen hypervisor, which works as trusted Agent,
to set permissions for the devices, passed-through to the Guest Domains,
which are non-trusted Agents. Trusted Agent will use xen,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].

xen,scmi-devid in Device-tree node example:
usb@...90000
{
    xen,scmi-devid = <19>;
    clocks = <&scmi_clock 3>, <&scmi_clock 2>;
    resets = <&scmi_reset 10>, <&scmi_reset 9>;
    power-domains = <&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 xen,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 xen,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 xen,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

Oleksii Moisieiev (2):
  dt-bindings: Add vendor prefix for Xen hypervisor
  dt-bindings: xen: Add xen,scmi-devid property description for SCMI

 .../bindings/firmware/xen,scmi-devid.yaml     | 42 +++++++++++++++++++
 .../devicetree/bindings/vendor-prefixes.yaml  |  2 +
 2 files changed, 44 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/firmware/xen,scmi-devid.yaml

-- 
2.27.0