https://www.kernel.org/doc/html/latest/staging/tee.html
User space Kernel Secure world
~~~~~~~~~~ ~~~~~~ ~~~~~~~~~~~~
+--------+ +-------------+
| Client | | Trusted |
+--------+ | Application |
/\ +-------------+
|| +----------+ /\
|| |tee- | ||
|| |supplicant| \/
|| +----------+ +-------------+
\/ /\ | TEE Internal|
+-------+ || | API |
+ TEE | || +--------+--------+ +-------------+
| Client| || | TEE | OP-TEE | | OP-TEE |
| API | \/ | subsys | driver | | Trusted OS |
+-------+----------------+----+-------+----+-----------+-------------+
| Generic TEE API | | OP-TEE MSG |
| IOCTL (TEE_IOC_*) | | SMCCC (OPTEE_SMC_CALL_*) |
+-----------------------------+ +------------------------------+