[PATCH 3/3] Documentation: tee: Add TS-TEE driver

[Balint Dobszay]

Add documentation for the Trusted Services TEE driver.

Signed-off-by: Balint Dobszay <balint.dobszay at arm.com>
---
 Documentation/tee/index.rst  |  1 +
 Documentation/tee/ts-tee.rst | 70 ++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 Documentation/tee/ts-tee.rst

diff --git a/Documentation/tee/index.rst b/Documentation/tee/index.rst
index a23bd08847e5..4be6e69d7837 100644
--- a/Documentation/tee/index.rst
+++ b/Documentation/tee/index.rst
@@ -10,6 +10,7 @@ TEE Subsystem
    tee
    op-tee
    amd-tee
+   ts-tee
 
 .. only::  subproject and html
 
diff --git a/Documentation/tee/ts-tee.rst b/Documentation/tee/ts-tee.rst
new file mode 100644
index 000000000000..e121ebbbfab7
--- /dev/null
+++ b/Documentation/tee/ts-tee.rst
@@ -0,0 +1,70 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+TS-TEE (Trusted Services project)
+=================================
+
+This driver provides access to secure services implemented by Trusted Services.
+
+Trusted Services [1] is a TrustedFirmware.org project that provides a framework
+for developing and deploying device Root of Trust services in FF-A [2] S-EL0
+Secure Partitions. The project hosts the reference implementation of the Arm
+Platform Security Architecture [3] for Arm A-profile devices.
+
+The FF-A Secure Partitions (SP) are accessible through the FF-A driver [4] which
+provides the low level communication for this driver. On top of that the Trusted
+Services RPC protocol is used [5]. To use the driver from user space a reference
+implementation is provided at [6], which is part of the Trusted Services client
+library called libts [7].
+
+All Trusted Services (TS) SPs have the same FF-A UUID, it identifies the TS RPC
+protocol. A TS SP can host one or more services (e.g. PSA Crypto, PSA ITS, etc).
+A service is identified by its service UUID, the same type of service cannot be
+present twice in the same SP. During SP boot each service in the SP is assigned
+an "interface ID", this is just a short ID to simplify message addressing.
+
+The generic TEE design is to share memory at once with the TEE implementation,
+which can then be reused to communicate with multiple TAs. However, in case of
+FF-A, memory sharing works on an endpoint level, i.e. memory is shared with a
+specific SP. User space has to be able to separately share memory with each SP
+based on its endpoint ID, therefore a separate TEE device is registered for each
+discovered TS SP. Opening the SP corresponds to opening the TEE device and
+creating a TEE context. A TS SP hosts one or more services, opening a service
+corresponds to opening a session in the given tee_context.
+
+Overview of a system with Trusted Services components::
+
+   User space                  Kernel space                   Secure world
+   ~~~~~~~~~~                  ~~~~~~~~~~~~                   ~~~~~~~~~~~~
+   +--------+                                               +-------------+
+   | Client |                                               | Trusted     |
+   +--------+                                               | Services SP |
+      /\                                                    +-------------+
+      ||                                                          /\
+      ||                                                          ||
+      ||                                                          ||
+      \/                                                          \/
+   +-------+                +----------+--------+           +-------------+
+   | libts |                |  TEE     | TS-TEE |           |  FF-A SPMC  |
+   |       |                |  subsys  | driver |           |   + SPMD    |
+   +-------+----------------+----+-----+--------+-----------+-------------+
+   |      Generic TEE API        |     |  FF-A  |     TS RPC protocol     |
+   |      IOCTL (TEE_IOC_*)      |     | driver |        over FF-A        |
+   +-----------------------------+     +--------+-------------------------+
+
+References
+==========
+
+[1] https://www.trustedfirmware.org/projects/trusted-services/
+
+[2] https://developer.arm.com/documentation/den0077/
+
+[3] https://www.arm.com/architecture/security-features/platform-security
+
+[4] drivers/firmware/arm_ffa/
+
+[5] https://trusted-services.readthedocs.io/en/v1.0.0/developer/service-access-protocols.html#abi
+
+[6] https://git.trustedfirmware.org/TS/trusted-services.git/tree/components/rpc/ts_rpc/caller/linux/ts_rpc_caller_linux.c?h=v1.0.0
+
+[7] https://git.trustedfirmware.org/TS/trusted-services.git/tree/deployments/libts/arm-linux/CMakeLists.txt?h=v1.0.0
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