[PATCH v4 11/11] Documentation: tee: Add Qualcomm TEE driver

Amirreza Zarrabi
2025-04-29T06:07:16Z

Add documentation for the Qualcomm TEE driver.

Signed-off-by: Amirreza Zarrabi <amirreza.zarrabi@oss.qualcomm.com>
---
Documentation/tee/index.rst | 1 +
Documentation/tee/qtee.rst | 150 ++++++++++++++++++++++++++++++++++++++++++++
MAINTAINERS | 1 +
3 files changed, 152 insertions(+)

diff --git a/Documentation/tee/index.rst b/Documentation/tee/index.rst
index 4be6e69d7837..62afb7ee9b52 100644
--- a/Documentation/tee/index.rst
+++ b/Documentation/tee/index.rst
@@ -11,6 +11,7 @@ TEE Subsystem
op-tee
amd-tee
ts-tee
+ qtee

.. only:: subproject and html

diff --git a/Documentation/tee/qtee.rst b/Documentation/tee/qtee.rst
new file mode 100644
index 000000000000..8ae4da17c3a7
--- /dev/null
+++ b/Documentation/tee/qtee.rst
@@ -0,0 +1,150 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============================================
+QTEE (Qualcomm Trusted Execution Environment)
+=============================================
+
+The QTEE driver handles communication with Qualcomm TEE [1].
+
+The lowest level of communication with QTEE builds on the ARM SMC Calling
+Convention (SMCCC) [2], which is the foundation for QTEE's Secure Channel
+Manager (SCM) [3] used internally by the driver [4].
+
+In a QTEE-based system, services are represented as objects with a series of
+operations that can be called to produce results, including other objects.
+
+When an object is hosted within QTEE, executing its operations is referred
+to as direct invocation. QTEE can invoke objects hosted in the kernel or
+userspace using a method known as callback requests.
+
+The SCM provides two functions for direct invocation and callback request:
+
+- QCOM_SCM_SMCINVOKE_INVOKE for direct invocation. It can return either
+ a result or a callback request.
+- QCOM_SCM_SMCINVOKE_CB_RSP submits a response for a previous callback request.
+
+The QTEE Transport Message [5] is stacked on top of the SCM driver functions.
+
+A message consists of two buffers shared with QTEE: inbound and outbound
+buffers. The inbound buffer is used for direct invocation, and the outbound
+buffer is used to make callback requests. This picture shows the contents of
+a QTEE transport message::
+
+ +---------------------+
+ | v
+ +-----------------+-------+-------+------+--------------------------+
+ | qcomtee_msg_ |object | buffer | |
+ | object_invoke | id | offset, size | | (inbound buffer)
+ +-----------------+-------+--------------+--------------------------+
+ <---- header -----><---- arguments ------><- in/out buffer payload ->
+
+ +-----------+
+ | v
+ +-----------------+-------+-------+------+----------------------+
+ | qcomtee_msg_ |object | buffer | |
+ | callback | id | offset, size | | (outbound buffer)
+ +-----------------+-------+--------------+----------------------+
+
+Each buffer is started with a header and array of arguments.
+
+QTEE Transport Message supports four types of arguments:
+
+- Input Object (IO) is an object parameter to the current invocation
+ or callback request.
+- Output Object (OO) is an object parameter from the current invocation
+ or callback request.
+- Input Buffer (IB) is (offset, size) pair to the inbound or outbound region
+ to store parameter to the current invocation or callback request.
+- Output Buffer (OB) is (offset, size) pair to the inbound or outbound region
+ to store parameter from the current invocation or callback request.
+
+The QTEE driver provides the qcomtee_object, which represents an object within
+both QTEE and the kernel. To access any service in QTEE, a client needs to
+invoke an instance of this object. Any structure intended to represent a service
+for export to QTEE should include an instance of qcomtee_object::
+
+ struct driver_service {
+ struct qcomtee_object object;
+ ...
+ };
+
+ #define to_driver_service_object(o) container_of((o), struct driver_service, object)
+
+ static int driver_service_dispatch(struct qcomtee_object *object, u32 op,
+ struct qcomtee_arg *args)
+ {
+ struct driver_service *so = to_driver_service_object(object);
+
+ switch(op) {
+ case OBJECT_OP1:
+ ...
+ break;
+ default:
+ return -EINVAL;
+ }
+ }
+
+ static void driver_service_object_release(struct si_object *object)
+ {
+ struct driver_service *so = to_driver_service_object(object);
+ kfree(so);
+ }
+
+ struct si_object_operations driver_service_ops = {
+ .release = driver_service_object_release;
+ .dispatch = driver_service_dispatch;
+ };
+
+ void service_init(void)
+ {
+ struct driver_service *so = kzalloc(sizeof(*so), GFP_KERNEL);
+
+ /* Initialize so->object as a callback object. */
+ qcomtee_object_user_init(&so->object, QCOMTEE_OBJECT_TYPE_CB_OBJECT,
+ &driver_service_ops, "driver_service_object");
+
+ /* Invoke a QTEE object and pass/register 'so->object' with QTEE. */
+ ...
+ }
+ module_init(service_init);
+
+The QTEE driver utilizes qcomtee_object to encapsulate userspace objects. When
+a callback request is made, it translates into calling the dispatch operation.
+For userspace objects, this is converted into requests accessible to callback
+servers and available through generic TEE API IOCTLs.
+
+Picture of the relationship between the different components in the QTEE
+architecture::
+
+ User space Kernel Secure world
+ ~~~~~~~~~~ ~~~~~~ ~~~~~~~~~~~~
+ +--------+ +----------+ +--------------+
+ | Client | |callback | | Trusted |
+ +--------+ |server | | Application |
+ /\ +----------+ +--------------+
+ || +----------+ /\ /\
+ || |callback | || ||
+ || |server | || \/
+ || +----------+ || +--------------+
+ \/ /\ || | TEE Internal |
+ +-------+ || || | API |
+ | TEE | || || +--------+--------+ +--------------+
+ | Client| || || | TEE | QTEE | | QTEE |
+ | API | \/ \/ | subsys | driver | | Trusted OS |
+ +-------+----------------+----+-------+----+-------------+--------------+
+ | Generic TEE API | | QTEE MSG |
+ | IOCTL (TEE_IOC_*) | | SMCCC (QCOM_SCM_SMCINVOKE_*) |
+ +-----------------------------+ +---------------------------------+
+
+References
+==========
+
+[1] https://docs.qualcomm.com/bundle/publicresource/topics/80-70015-11/qualcomm-trusted-execution-environment.html
+
+[2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
+
+[3] drivers/firmware/qcom/qcom_scm.c
+
+[4] drivers/tee/qcomtee/qcom_scm.c
+
+[5] drivers/tee/qcomtee/qcomtee_msg.h
diff --git a/MAINTAINERS b/MAINTAINERS
index 88a9ad34bcf6..79259219d292 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20261,6 +20261,7 @@ QUALCOMM TEE (QCOMTEE) DRIVER
M: Amirreza Zarrabi <amirreza.zarrabi@oss.qualcomm.com>
L: linux-arm-msm@vger.kernel.org
S: Maintained
+F: Documentation/tee/qtee.rst
F: drivers/tee/qcomtee/
F: include/linux/firmware/qcom/qcom_tee.h

--
2.34.1