[RFC PATCH v1 5/6] dt-bindings: firmware: add OP-TEE over the RISC-V RPMI TEE service group

[marouene . boubakri]

From: Marouene Boubakri <marouene.boubakri@xxxxxxxxxxx>

On RISC-V, OP-TEE runs as a supervisor domain isolated from the Rich
Execution Environment by the M-mode firmware. There is no SMC or HVC
instruction to reach it: the kernel invokes OP-TEE through the TEE
service group of the RISC-V Platform Management Interface (RPMI) v2.0,
carried on an SBI Message Proxy (MPXY) channel. Each call is a TEE_CALL
service request whose service data carries the register arguments of
the OP-TEE SMC ABI, so the ABI itself is unchanged from Arm.

Add a binding for such an OP-TEE instance. The compatible string keeps
the "linaro" vendor prefix of "linaro,optee-tz" which identifies the
OP-TEE reference implementation. The node references the MPXY mailbox
channel implementing the TEE service group, and carries the endpoint
identifiers assigned by the RPMI TEE framework to the REE and to OP-TEE
since the framework does not define any way for an endpoint to learn
them other than the optional TEE_PROBE_SYSTEM service, whose CBOR
encoded response cannot be parsed in the kernel.

Signed-off-by: Marouene Boubakri <marouene.boubakri@xxxxxxxxxxx>
---
 .../bindings/firmware/linaro,optee-rpmi.yaml  | 79 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 80 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/firmware/linaro,optee-rpmi.yaml

diff --git a/Documentation/devicetree/bindings/firmware/linaro,optee-rpmi.yaml b/Documentation/devicetree/bindings/firmware/linaro,optee-rpmi.yaml
new file mode 100644
index 000000000..1c3dffc33
--- /dev/null
+++ b/Documentation/devicetree/bindings/firmware/linaro,optee-rpmi.yaml
@@ -0,0 +1,79 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/firmware/linaro,optee-rpmi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: OP-TEE accessed through the RISC-V RPMI TEE service group
+
+maintainers:
+  - Marouene Boubakri <marouene.boubakri@xxxxxxxxxxx>
+
+description: |
+  OP-TEE is a piece of software using hardware features to provide a Trusted
+  Execution Environment. On RISC-V, OP-TEE runs as a supervisor domain
+  isolated from the Rich Execution Environment (REE) by the M-mode firmware.
+
+  The REE reaches OP-TEE through the TEE service group of the RISC-V Platform
+  Management Interface (RPMI) [1], carried on a channel of the SBI Message
+  Proxy (MPXY) extension [2]. Each call into OP-TEE is a TEE_CALL service
+  request whose service data carries the register arguments of the OP-TEE
+  SMC ABI (drivers/tee/optee/optee_smc.h), as described in
+  drivers/tee/optee/optee_rpmi.h.
+
+  The RPMI TEE framework (the M-mode firmware) assigns an identifier to each
+  endpoint. The identifiers of the REE and of OP-TEE are required to
+  address TEE_CALL requests and are described here.
+
+  The compatible string uses the same "linaro" vendor prefix as
+  "linaro,optee-tz", which identifies the OP-TEE reference implementation.
+
+  [1] RISC-V Platform Management Interface (RPMI) v2.0 (or higher)
+      https://github.com/riscv-non-isa/riscv-rpmi/releases
+
+  [2] RISC-V Supervisor Binary Interface (SBI) v3.0 (or higher)
+      https://github.com/riscv-non-isa/riscv-sbi-doc/releases
+
+properties:
+  $nodename:
+    const: optee
+
+  compatible:
+    const: linaro,optee-rpmi
+
+  mboxes:
+    maxItems: 1
+    description:
+      SBI MPXY channel implementing the RPMI TEE service group.
+
+  riscv,rpmi-tee-sender-id:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Endpoint identifier of the REE, used as SENDER_ID of the TEE_CALL
+      requests.
+
+  riscv,rpmi-tee-target-id:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Endpoint identifier of OP-TEE, used as TARGET_ID of the TEE_CALL
+      requests.
+
+required:
+  - compatible
+  - mboxes
+  - riscv,rpmi-tee-sender-id
+  - riscv,rpmi-tee-target-id
+
+additionalProperties: false
+
+examples:
+  - |
+    firmware {
+        optee {
+            compatible = "linaro,optee-rpmi";
+            mboxes = <&mpxy_mbox 0x10 0x0>;
+            riscv,rpmi-tee-sender-id = <0>;
+            riscv,rpmi-tee-target-id = <1>;
+        };
+    };
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index 44860f991..bf4884f34 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20415,6 +20415,7 @@ M:	Jens Wiklander <jenswi@xxxxxxxxxx>
 L:	op-tee@xxxxxxxxxxxxxxxxxxxxxxxxx (moderated for non-subscribers)
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-bus-optee-devices
+F:	Documentation/devicetree/bindings/firmware/linaro,optee-rpmi.yaml
 F:	drivers/tee/optee/
 
 OP-TEE RANDOM NUMBER GENERATOR (RNG) DRIVER
-- 
2.43.0