[PATCH v2 1/5] Documentation/firmware: add imx/se to other_interfaces

From: Pankaj Gupta
Date: Thu May 23 2024 - 06:52:53 EST

Documents i.MX SoC's Service layer and C_DEV driver for selected SoC(s)
that contains the NXP hardware IP(s) for secure-enclaves(se) like:
- NXP EdgeLock Enclave on i.MX93 & i.MX8ULP

Signed-off-by: Pankaj Gupta <pankaj.gupta@xxxxxxx>
---
.../driver-api/firmware/other_interfaces.rst | 119 +++++++++++++++++++++
1 file changed, 119 insertions(+)

diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst
index 06ac89adaafb..65e69396e22a 100644
--- a/Documentation/driver-api/firmware/other_interfaces.rst
+++ b/Documentation/driver-api/firmware/other_interfaces.rst
@@ -49,3 +49,122 @@ of the requests on to a secure monitor (EL3).

.. kernel-doc:: drivers/firmware/stratix10-svc.c
:export:
+
+NXP Secure Enclave Firmware Interface
+=====================================
+
+Introduction
+------------
+The NXP's i.MX HW IP like EdgeLock-Enclave, V2X etc., creates an embedded secure
+enclave within the SoC boundary to enable features like
+ - Hardware Security Module (HSM)
+ - Security Hardware Extension (SHE)
+ - Vehicular to Anything (V2X)
+
+Each of the above feature, is enabled through dedicated NXP H/W IP on the SoC.
+On a single SoC, multiple hardware IP (or can say more than one secure enclave)
+can exists.
+
+NXP SoCs enabled with the such secure enclaves(SEs) IPs are:
+i.MX93, i.MX8ULP
+
+To communicate with one or more co-existing SE(s) on SoC, there is/are dedicated
+messaging units(MU) per SE. Each co-existing 'se' can have one or multiple exclusive
+MU(s), dedicated to itself. None of the MU is shared between two SEs.
+Communication of the MU is realized using the Linux mailbox driver.
+
+NXP Secure Enclave(SE) Interface
+--------------------------------
+All those SE interfaces 'se-if' that is/are dedicated to a particular SE, will be
+enumerated and provisioned under the very single 'SE' node.
+
+Each 'se-if', comprise of twp layers:
+- (C_DEV Layer) User-Space software-access interface.
+- (Service Layer) OS-level software-access interface.
+
+ +--------------------------------------------+
+ | Character Device(C_DEV) |
+ | |
+ | +---------+ +---------+ +---------+ |
+ | | misc #1 | | misc #2 | ... | misc #n | |
+ | | dev | | dev | | dev | |
+ | +---------+ +---------+ +---------+ |
+ | +-------------------------+ |
+ | | Misc. Dev Synchr. Logic | |
+ | +-------------------------+ |
+ | |
+ +--------------------------------------------+
+
+ +--------------------------------------------+
+ | Service Layer |
+ | |
+ | +-----------------------------+ |
+ | | Message Serialization Logic | |
+ | +-----------------------------+ |
+ | +---------------+ |
+ | | imx-mailbox | |
+ | | mailbox.c | |
+ | +---------------+ |
+ | |
+ +--------------------------------------------+
+
+- service layer:
+ This layer is responsible for ensuring the communication protocol, that is defined
+ for communication with firmware.
+
+ FW Communication protocol ensures two things:
+ - Serializing the messages to be sent over an MU.
+
+ - FW can handle one command-message at a time.
+
+- c_dev:
+ This layer offers character device contexts, created as '/dev/<se>_mux_chx'.
+ Using these multiple device contexts, that are getting multiplexed over a single MU,
+ user-space application(s) can call fops like write/read to send the command-message,
+ and read back the command-response-message to/from Firmware.
+ fops like read & write uses the above defined service layer API(s) to communicate with
+ Firmware.
+
+ Misc-device(/dev/<se>_mux_chn) synchronization protocol:
+
+ Non-Secure + Secure
+ |
+ |
+ +---------+ +-------------+ |
+ | se_fw.c +<---->+imx-mailbox.c| |
+ | | | mailbox.c +<-->+------+ +------+
+ +---+-----+ +-------------+ | MU X +<-->+ ELE |
+ | +------+ +------+
+ +----------------+ |
+ | | |
+ v v |
+ logical logical |
+ receiver waiter |
+ + + |
+ | | |
+ | | |
+ | +----+------+ |
+ | | | |
+ | | | |
+ device_ctx device_ctx device_ctx |
+ |
+ User 0 User 1 User Y |
+ +------+ +------+ +------+ |
+ |misc.c| |misc.c| |misc.c| |
+ kernel space +------+ +------+ +------+ |
+ |
+ +------------------------------------------------------ |
+ | | | |
+ userspace /dev/ele_muXch0 | | |
+ /dev/ele_muXch1 | |
+ /dev/ele_muXchY |
+ |
+
+When a user sends a command to the firmware, it registers its device_ctx
+as waiter of a response from firmware.
+
+Enclave's Firmware owns the storage management, over linux filesystem.
+For this c_dev provisions a dedicated slave device called "receiver".
+
+.. kernel-doc:: drivers/firmware/imx/se_fw.c
+ :export:

--
2.34.1