Most platforms now use OP-TEE early loading and we have gained support to communicate with OP-TEE and not only loading it. Reflect that in the docs. Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> --- Documentation/user/optee.rst | 45 +++++++++++++++++++++++++++--------- 1 file changed, 34 insertions(+), 11 deletions(-) diff --git a/Documentation/user/optee.rst b/Documentation/user/optee.rst index 950917b446ad..2729d21d2e44 100644 --- a/Documentation/user/optee.rst +++ b/Documentation/user/optee.rst @@ -4,20 +4,20 @@ OP-TEE ====== -Barebox is able to start the Open Portable Trusted Execution Environment -(OP-TEE) either before starting the linux kernel or during lowlevel board -initialization in the Pre Bootloader ``PBL``. +barebox has support for loading and communicating with the Open Portable Trusted +Execution Environment (OP-TEE). -Before Linux start ------------------- -Enable the `CONFIG_BOOTM_OPTEE` configuration variable and configure the -`CONFIG_OPTEE_SIZE` variable. This will reserve a memory area at the end -of memory for OP-TEE to run, usually Barebox would relocate itself there. To -load OP-TEE before the kernel is started, configure the global ``bootm.tee`` -variable to point to a valid OPTEE v1 binary. +Loading OP-TEE +-------------- + +barebox can start OP-TEE either during lowlevel board initialization +in the :ref:`prebootloader <pbl>` or prior to starting the linux kernel. + +.. _optee_early_loading: During the PBL --------------- +^^^^^^^^^^^^^^ + To start OP-TEE during the lowlevel initialization of your board in the ``PBL``, enable the ``CONFIG_PBL_OPTEE`` configuration variable. your board should then call the function ``start_optee_early(void* tee, void* fdt)`` with a valid tee @@ -27,3 +27,26 @@ Since OP-TEE in the default configuration also modifies the device tree, don't pass the barebox internal device tree, instead copy it into a different memory location and pass it to OP-TEE afterwards. The modified device tree can then be passed to the main barebox start function. + +Before Linux start +^^^^^^^^^^^^^^^^^^ + +.. warning:: Late loading of OP-TEE is deprecated, greatly increases the + attack surface and is only supported on 32-bit ARM systems. + Systems should prefer early loading OP-TEE whenever possible. + +Enable the `CONFIG_BOOTM_OPTEE` configuration variable and configure the +`CONFIG_OPTEE_SIZE` variable. This will reserve a memory area at the end +of memory for OP-TEE to run, usually Barebox would relocate itself there. To +load OP-TEE before the kernel is started, configure the global ``bootm.tee`` +variable to point to a valid OPTEE v1 binary. + +Communication with OP-TEE +------------------------- + +Controlled by the ``CONFIG_OPTEE`` option, barebox has support for +communicating with OP-TEE via secure monitor calls and dynamic shared memory. +This is possible independently of whether OP-TEE was loaded by barebox or not. + +The primary use cases currently is SCMI-over-OP-TEE, which is required on +the STM32MP13. -- 2.39.5
