Compilation of Optee-os (Trusted Execution Environment):
1. Pre-requisite
2. Initialise cross-compilation via SDK
3. Prepare optee-os source code
4. Management of optee-os source code
5. Compile optee-os source code
6. Update software on board

1. Pre-requisite:
-----------------
OpenSTLinux SDK must be installed.

If you have never configured you git configuration:
    $ git config --global user.name "your_name"
    $ git config --global user.email "your_email@example.com"

2. Initialise cross-compilation via SDK:
---------------------------------------
 Source SDK environment:
    $ source <path to SDK>/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi

 To verify if your cross-compilation environment have put in place:
    $ set | grep CROSS
    CROSS_COMPILE=arm-ostl-linux-gnueabi-

Warning: the environment are valid only on the shell session where you have
 sourced the sdk environment.

3. Prepare optee-os source:
------------------------
If you have the tarball and the list of patch then you must extract the
tarball and apply the patch.
    $> tar xfz ##BP##-##PR##.tar.gz
A new directory containing optee standard source code will be created, go into it:
    $> cd ##BP##

NB: if there is no git management on source code and you would like to have a git management
on the code see section 4 [Management of optee-os source code]
    if there is some patch, please apply it on source code
    $> for p in `ls -1 ../*.patch`; do patch -p1 < $p; done

4. Management of optee-os source code:
-----------------------------------
If you like to have a better management of change made on optee-os source,
you have 3 solutions to use git

4.1 Get STMicroelectronics optee-os source from GitHub
    URL: https://github.com/STMicroelectronics/optee_os.git
    Branch: ##ARCHIVER_ST_BRANCH##
    Revision: ##ARCHIVER_ST_REVISION##

    $ git clone https://github.com/STMicroelectronics/optee_os.git
    $ git checkout -b WORKING ##ARCHIVER_ST_REVISION##

4.2 Create Git from tarball
    $ cd <optee-os source>
    $ test -d .git || git init . && git add . && git commit -m "optee-os source code" && git gc
    $ git checkout -b WORKING
    $ for p in `ls -1 <path to patch>/*.patch`; do git am $p; done

MANDATORY: You must update sources
    $ cd <directory to optee-os source code>
    $ chmod 755 scripts/bin_to_c.py

4.3 Get Git from community and apply STMicroelectronics patches
    URL: git://github.com/OP-TEE/optee_os.git
    Branch: ##ARCHIVER_COMMUNITY_BRANCH##
    Revision: ##ARCHIVER_COMMUNITY_REVISION##

    $ git clone git://github.com/OP-TEE/optee_os.git
    $ cd <optee-os source>
    $ git checkout -b WORKING ##ARCHIVER_COMMUNITY_REVISION##
    $ for p in `ls -1 <path to patch>/*.patch`; do git am $p; done

MANDATORY: You must update sources
    $ cd <directory to optee-os source code>
    $ chmod 755 scripts/bin_to_c.py

5. Build optee-os source code:
--------------------------------
Since OpenSTLinux has activated FIP by default, so the FIP_artifacts should be specified before launching compilation
  - In case of using SOURCES-xxxx.tar.gz of Developer package the FIP_DEPLOYDIR_ROOT should be set as below:
    $> export FIP_DEPLOYDIR_ROOT=$PWD/../../FIP_artifacts

To compile optee-os source code
    $> make -f $PWD/../Makefile.sdk all
or for a specific config :
    $ make -f $PWD/../Makefile.sdk CFG_EMBED_DTB_SOURCE_FILE=stm32mp157c-ev1 all

The generated FIP images are available in $FIP_DEPLOYDIR_ROOT/fip


6. Update software on board:
----------------------------
Please use STM32CubeProgrammer and only tick the ssbl-boot and fip partitions (more informations on the wiki website http://wiki.st.com/stm32mpu)