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@nxp.com>
---
 .../driver-api/firmware/other_interfaces.rst       | 121 +++++++++++++++++++++
 1 file changed, 121 insertions(+)

diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst
index 06ac89adaafb..a3a95b54a174 100644
--- a/Documentation/driver-api/firmware/other_interfaces.rst
+++ b/Documentation/driver-api/firmware/other_interfaces.rst
@@ -49,3 +49,124 @@ 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 exist.
+
+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
+MUs, 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
+--------------------------------
+Although MU(s) is/are not shared between SE(s). But for SoC like i.MX95 which has
+multiple SE(s) like HSM, V2X-HSM, V2X-SHE; all the SE(s) and their interfaces 'se-if'
+that is/are dedicated to a particular SE will be enumerated and provisioned using the
+single compatible node("fsl,imx95-se").
+
+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,
+  userspace 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 use 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