Commit 2253bd84 authored by Sumit Garg's avatar Sumit Garg Committed by Jonathan Corbet
Browse files

Documentation: tee: Document TEE kernel interface 



Update documentation with TEE bus infrastructure which provides an
interface for kernel client drivers to communicate with corresponding
Trusted Application.

Signed-off-by: default avatarSumit Garg <sumit.garg@linaro.org>
Reviewed-by: default avatarMaxim Uvarov <maxim.uvarov@linaro.org>
Link: https://lore.kernel.org/r/1591253979-29067-1-git-send-email-sumit.garg@linaro.org


Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent cf37fc4a

Documentation/tee.txt

+68 −0
Original line number Diff line number Diff line
@@ -53,6 +53,66 @@ clients, forward them to the TEE and send back the results. In the case of 
supplicants the communication goes in the other direction, the TEE sends

requests to the supplicant which then sends back the result.



The TEE kernel interface

========================



Kernel provides a TEE bus infrastructure where a Trusted Application is

represented as a device identified via Universally Unique Identifier (UUID) and

client drivers register a table of supported device UUIDs.



TEE bus infrastructure registers following APIs:

-  match(): iterates over the client driver UUID table to find a corresponding

   match for device UUID. If a match is found, then this particular device is

   probed via corresponding probe API registered by the client driver. This

   process happens whenever a device or a client driver is registered with TEE

   bus.

-  uevent(): notifies user-space (udev) whenever a new device is registered on

   TEE bus for auto-loading of modularized client drivers.



TEE bus device enumeration is specific to underlying TEE implementation, so it

is left open for TEE drivers to provide corresponding implementation.



Then TEE client driver can talk to a matched Trusted Application using APIs

listed in include/linux/tee_drv.h.



TEE client driver example

-------------------------



Suppose a TEE client driver needs to communicate with a Trusted Application

having UUID: ``ac6a4085-0e82-4c33-bf98-8eb8e118b6c2``, so driver registration

snippet would look like::



	static const struct tee_client_device_id client_id_table[] = {

		{UUID_INIT(0xac6a4085, 0x0e82, 0x4c33,

			   0xbf, 0x98, 0x8e, 0xb8, 0xe1, 0x18, 0xb6, 0xc2)},

		{}

	};



	MODULE_DEVICE_TABLE(tee, client_id_table);



	static struct tee_client_driver client_driver = {

		.id_table	= client_id_table,

		.driver		= {

			.name		= DRIVER_NAME,

			.bus		= &tee_bus_type,

			.probe		= client_probe,

			.remove		= client_remove,

		},

	};



	static int __init client_init(void)

	{

		return driver_register(&client_driver.driver);

	}



	static void __exit client_exit(void)

	{

		driver_unregister(&client_driver.driver);

	}



	module_init(client_init);

	module_exit(client_exit);



OP-TEE driver

=============
@@ -112,6 +172,14 @@ kernel are handled by the kernel driver. Other RPC messages will be forwarded to 
tee-supplicant without further involvement of the driver, except switching

shared memory buffer representation.



OP-TEE device enumeration

-------------------------



OP-TEE provides a pseudo Trusted Application: drivers/tee/optee/device.c in

order to support device enumeration. In other words, OP-TEE driver invokes this

application to retrieve a list of Trusted Applications which can be registered

as devices on the TEE bus.



AMD-TEE driver

==============