[PATCH v4 0/2] dt-bindings: Intorduce domain-controller

Oleksii Moisieiev
2022-07-07T12:32:04Z

Introducing the domain controller provider/consumenr bindngs which allow to
divided system on chip into multiple domains that can be used to select
by who hardware blocks could be accessed.
A domain could be a cluster of CPUs, a group of hardware blocks or the
set of devices, passed-through to the Guest in the virtualized systems.

Device controllers are typically used to set the permissions of the hardware
block. The contents of the domain configuration properties are defined by the
binding for the individual domain controller device.

The device controller conception in the virtualized systems is to set
the device configuration for SCMI (System Control and Management
Interface) which controls clocks/power-domains/resets etc from the
Firmware. This configuratio sets the device_id to set the device permissions
for the Fimware using BASE_SET_DEVICE_PERMISSIONS message (see 4.2.2.10 of [0]).
There is no BASE_GET_DEVICE_PERMISSIONS call in SCMI and the way to
determine device_id is not covered by the specification.
Device permissions management described in DEN 0056, Section 4.2.2.10 [0].
Given parameter should set the device_id, needed to set device
permissions in the Firmware.
This property is used by trusted Agent (which is hypervisor in our case)
to set permissions for the devices, passed-through to the non-trusted
Agents. Trusted Agent will use device-perms 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].

Domains in Device-tree node example:
usb@e6590000
{
domain-0 = <&scmi 19>; //Set domain id 19 to usb node
clocks = <&scmi_clock 3>, <&scmi_clock 2>;
resets = <&scmi_reset 10>, <&scmi_reset 9>;
power-domains = <&scmi_power 0>;
};

&scmi {
#domain-cells = <1>;
}

All mentioned bindings are going to be processed by XEN SCMI mediator
feature, which is responsible to redirect SCMI calls from guests to the
firmware, and not going be passed to the guests.

Domain-controller provider/consumenr concept was taken from the bus
controller framework patch series, provided in the following thread:
[1].

I think we can cooperate with the bus controller framework developers
and produce the common binding, which will fit the requirements of both
features

Also, I think that binding can also be used for STM32 ETZPC bus
controller feature, proposed in the following thread: [2].

Looking forward for your thoughts and ideas.

[0] https://developer.arm.com/documentation/den0056/latest
[1] https://lore.kernel.org/all/20190318100605.29120-1-benjamin.gaignard@st.com/
[2] https://lore.kernel.org/all/20200701132523.32533-1-benjamin.gaignard@st.com/

---
Changes v1 -> V2:
- update parameter name, made it xen-specific
- add xen vendor bindings

Changes V2 -> V3:
- update parameter name, make it generic
- update parameter format, add link to controller
- do not include xen vendor bindings as already upstreamed

Changes V3 -> V4:
- introduce domain controller provider/consumer device tree bindings
- making scmi node to act as domain controller provider when the
device permissions should be configured
---

Oleksii Moisieiev (2):
dt-bindings: Document common device controller bindings
dt-bindings: Update scmi node description

.../bindings/domains/domain-controller.yaml | 80 +++++++++++++++++++
.../bindings/firmware/arm,scmi.yaml | 25 ++++++
2 files changed, 105 insertions(+)
create mode 100644 Documentation/devicetree/bindings/domains/domain-controller.yaml

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2.27.0