On Mon, May 26, 2025 at 11:56:57PM -0700, Amirreza Zarrabi wrote:
> Add documentation for the Qualcomm TEE driver.
>
> Signed-off-by: Amirreza Zarrabi <amirreza.zarrabi@xxxxxxxxxxxxxxxx>
> ---
> 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);
Lets drop any reference for kernel client/services since they aren't
supported by this patch-set yet.
-Sumit
> +
> +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 99fe1ae22ae0..42823d33cc03 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -20515,6 +20515,7 @@ QUALCOMM TEE (QCOMTEE) DRIVER
> M: Amirreza Zarrabi <amirreza.zarrabi@xxxxxxxxxxxxxxxx>
> L: linux-arm-msm@xxxxxxxxxxxxxxx
> S: Maintained
> +F: Documentation/tee/qtee.rst
> F: drivers/tee/qcomtee/
> F: include/linux/firmware/qcom/qcom_tee.h
>
>
> --
> 2.34.1
>
