Feature Overview
================

This page provides an overview of the current |TF-A| feature set. For a full
description of these features and their implementation details, please see
the documents that are part of the *Components* and *System Design* chapters.

The :ref:`Change Log & Release Notes` provides details of changes made since the
last release.

Current features
----------------

- Initialization of the secure world, for example exception vectors, control
registers and interrupts for the platform.

- Library support for CPU specific reset and power down sequences. This
includes support for errata workarounds and the latest Arm DynamIQ CPUs.

- Drivers to enable standard initialization of Arm System IP, for example
Generic Interrupt Controller (GIC), Cache Coherent Interconnect (CCI),
Cache Coherent Network (CCN), Network Interconnect (NIC) and TrustZone
Controller (TZC).

- Secure Monitor library code such as world switching, EL2/EL1 context
management and interrupt routing.

- SMC (Secure Monitor Call) handling, conforming to the `SMC Calling
Convention`_ using an EL3 runtime services framework.

- |PSCI| library support for CPU, cluster and system power management
use-cases.
This library is pre-integrated with the AArch64 EL3 Runtime Software, and
is also suitable for integration with other AArch32 EL3 Runtime Software,
for example an AArch32 Secure OS.

- A generic |SCMI| driver to interface with conforming power controllers, for
example the Arm System Control Processor (SCP).

- A minimal AArch32 Secure Payload (*SP_MIN*) to demonstrate |PSCI| library
integration with AArch32 EL3 Runtime Software.

- Secure partition manager dispatcher(SPMD) with following two configurations:

- S-EL2 SPMC implementation, widely compliant with FF-A v1.1 EAC0 and initial
support of FF-A v1.2.

- EL3 SPMC implementation, compliant with a subset of FF-A v1.1 EAC0.

- Support for Arm CCA based on FEAT_RME which supports authenticated boot and
execution of RMM with the necessary routing of RMI commands as specified in
RMM Beta 0 Specification.

- A Test SP and SPD to demonstrate AArch64 Secure Monitor functionality and SP
interaction with PSCI.

- SPDs for the `OP-TEE Secure OS`_, `NVIDIA Trusted Little Kernel`_,
`Trusty Secure OS`_ and `ProvenCore Secure OS`_.

- A Trusted Board Boot implementation, conforming to all mandatory TBBR
requirements. This includes image authentication, Firmware recovery,
Firmware encryption and packaging of the various firmware images into a
Firmware Image Package (FIP).

- Measured boot support with PoC to showcase its interaction with firmware TPM
(fTPM) service implemneted on top of OP-TEE.

- Support for Dynamic Root of Trust for Measurement (DRTM).

- Following firmware update mechanisms available:

- PSA Firmware Update (PSA FWU)

- TBBR Firmware Update (TBBR FWU)

- Reliability, Availability, and Serviceability (RAS) functionality, including

- A Secure Partition Manager (SPM) to manage Secure Partitions in
Secure-EL0, which can be used to implement simple management and
security services.

- An |SDEI| dispatcher to route interrupt-based |SDEI| events.

- An Exception Handling Framework (EHF) that allows dispatching of EL3
interrupts to their registered handlers, to facilitate firmware-first
error handling.

- A dynamic configuration framework that enables each of the firmware images
to be configured at runtime if required by the platform. It also enables
loading of a hardware configuration (for example, a kernel device tree)
as part of the FIP, to be passed through the firmware stages.
This feature is now incorporated inside the firmware configuration framework
(fconf).

- Support for alternative boot flows, for example to support platforms where
the EL3 Runtime Software is loaded using other firmware or a separate
secure system processor, or where a non-TF-A ROM expects BL2 to be loaded
at EL3.

- Support for Errata management firmware interface.

- Support for the GCC, LLVM and Arm Compiler 6 toolchains.

- Support for combining several libraries into a "romlib" image that may be
shared across images to reduce memory footprint. The romlib image is stored
in ROM but is accessed through a jump-table that may be stored
in read-write memory, allowing for the library code to be patched.

- Position-Independent Executable (PIE) support.

Experimental features
---------------------

A feature is considered experimental when still in development or isn't known
to the TF-A team as widely deployed or proven on end products. It is generally
advised such options aren't pulled into real deployments, or done with the
appropriate level of supplementary integration testing.

A feature is no longer considered experimental when it is generally agreed
the said feature has reached a level of maturity and quality comparable to
other features that have been integrated into products.

Experimental build options are found in following section
:ref:`build_options_experimental`. Their use through the build emits a warning
message.

Additionally the following libraries are marked experimental when included
in a platform:

- MPU translation library ``lib/xlat_mpu``
- RSE comms driver ``drivers/arm/rse``

Still to come
-------------

- Support for additional platforms.

- Documentation enhancements.

- Ongoing support for new architectural features, CPUs and System IP.

- Ongoing support for new Arm system architecture specifications.

- Ongoing security hardening, optimization and quality improvements.

.. _SMC Calling Convention: https://developer.arm.com/docs/den0028/latest
.. _OP-TEE Secure OS: https://github.com/OP-TEE/optee_os
.. _NVIDIA Trusted Little Kernel: http://nv-tegra.nvidia.com/gitweb/?p=3rdparty/ote_partner/tlk.git;a=summary
.. _Trusty Secure OS: https://source.android.com/security/trusty
.. _ProvenCore Secure OS: https://provenrun.com/products/provencore/

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