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Subject[RFC PATCH v3 4/4] Documentation: tee: add AMD-TEE driver details
Date
Update tee.txt with AMD-TEE driver details. The driver is written
to communicate with AMD's TEE.

Co-developed-by: Devaraj Rangasamy <Devaraj.Rangasamy@amd.com>
Signed-off-by: Devaraj Rangasamy <Devaraj.Rangasamy@amd.com>
Signed-off-by: Rijo Thomas <Rijo-john.Thomas@amd.com>
---
Documentation/tee.txt | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 81 insertions(+)

diff --git a/Documentation/tee.txt b/Documentation/tee.txt
index afacdf2..c8fad81 100644
--- a/Documentation/tee.txt
+++ b/Documentation/tee.txt
@@ -112,6 +112,83 @@ 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.

+AMD-TEE driver
+==============
+
+The AMD-TEE driver handles the communication with AMD's TEE environment. The
+TEE environment is provided by AMD Secure Processor.
+
+The AMD Secure Processor (formerly called Platform Security Processor or PSP)
+is a dedicated processor that features ARM TrustZone technology, along with a
+software-based Trusted Execution Environment (TEE) designed to enable
+third-party Trusted Applications. This feature is currently enabled only for
+APUs.
+
+The following picture shows a high level overview of AMD-TEE::
+
+ |
+ x86 |
+ |
+ User space (Kernel space) | AMD Secure Processor (PSP)
+ ~~~~~~~~~~ ~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~~~~~~~~~
+ |
+ +--------+ | +-------------+
+ | Client | | | Trusted |
+ +--------+ | | Application |
+ /\ | +-------------+
+ || | /\
+ || | ||
+ || | \/
+ || | +----------+
+ || | | TEE |
+ || | | Internal |
+ \/ | | API |
+ +---------+ +-----------+---------+ +----------+
+ | TEE | | TEE | AMD-TEE | | AMD-TEE |
+ | Client | | subsystem | driver | | Trusted |
+ | API | | | | | OS |
+ +---------+-----------+----+------+---------+---------+----------+
+ | Generic TEE API | | ASP | Mailbox |
+ | IOCTL (TEE_IOC_*) | | driver | Register Protocol |
+ +--------------------------+ +---------+--------------------+
+
+At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the
+CPU to PSP mailbox regsister to submit commands to the PSP. The format of the
+command buffer is opaque to the ASP driver. It's role is to submit commands to
+the secure processor and return results to AMD-TEE driver. The interface
+between AMD-TEE driver and AMD Secure Processor driver can be found in [6].
+
+The AMD-TEE driver packages the command buffer payload for processing in TEE.
+The command buffer format for the different TEE commands can be found in [7].
+
+The TEE commands supported by AMD-TEE Trusted OS are:
+* TEE_CMD_ID_LOAD_TA - loads a Trusted Application (TA) binary into
+ TEE environment.
+* TEE_CMD_ID_UNLOAD_TA - unloads TA binary from TEE environment.
+* TEE_CMD_ID_OPEN_SESSION - opens a session with a loaded TA.
+* TEE_CMD_ID_CLOSE_SESSION - closes session with loaded TA
+* TEE_CMD_ID_INVOKE_CMD - invokes a command with loaded TA
+* TEE_CMD_ID_MAP_SHARED_MEM - maps shared memory
+* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory
+
+AMD-TEE Trusted OS is the firmware running on AMD Secure Processor.
+
+The AMD-TEE driver registers itself with TEE subsystem and implements the
+following driver function callbacks:
+
+* get_version - returns the driver implementation id and capability.
+* open - sets up the driver context data structure.
+* release - frees up driver resources.
+* open_session - loads the TA binary and opens session with loaded TA.
+* close_session - closes session with loaded TA and unloads it.
+* invoke_func - invokes a command with loaded TA.
+
+cancel_req driver callback is not supported by AMD-TEE.
+
+The GlobalPlatform TEE Client API [5] can be used by the user space (client) to
+talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening
+a session, invoking commands and clossing session with TA.
+
References
==========

@@ -125,3 +202,7 @@ References

[5] http://www.globalplatform.org/specificationsdevice.asp look for
"TEE Client API Specification v1.0" and click download.
+
+[6] include/linux/psp-tee.h
+
+[7] drivers/tee/amdtee/amdtee_if.h
--
1.9.1
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