Arm Firmware Framework for Arm A-profile (FF-A) support library

Arm Firmware Framework for Arm A-profile (FF-A) specification

FF-A Memory Management Protocol specification

Library for handling common FF-A related functionality, create and parse interfaces and descriptors defined by FF-A. Starting from FF-A v1.2 the memory management related parts of the specification have been moved to a separate document (link above).

Design goals

• Keep the code exception level agnostic by default. If exception level specific parts are inevitable, make it optional via a feature flag.
• Keep the code no_std compatible. Use only core by default, make parts using alloc optional via a feature flag.
• The interface towards the library's users should be ergonomic Rust and following Rust best-practices where possible.
  • Incorrect usage of this library when creating/packing/serializing data structures provided by this library is seen as a programmer error and the library will panic.
  • Parsing/unpacking/deserializing data structures provided by this library from a buffer is seen as runtime "user input data", and the library should make all necessary checks to validate the data. In this case the library should never panic, but return rich error types (preferably use thiserror) so the library user knows what's wrong.
• The FF-A descriptors, packed structs and bit shifting magic should be private for the library, never exposed to the library user (i.e. ffa_v1_1 and later modules).
  • The implementation of such data structures should strictly follow the FF-A specification.
  • Preferably write a doc comment for each such definition that specifies where it comes from in the spec (i.e. Table x.y or chapter x.y.z)
  • The data structures should derive the necessary zerocopy traits.

FF-A version handling

The FF-A specification allows different components of a system to use different versions of the specification. The version used at a specific FF-A instance (i.e. an interface between two FF-A components) is discovered at runtime, either by parsing FF-A manifests or using FFA_VERSION. The FF-A specification's minor version updates usually introduce changes in a way that the message encoding and parsing stays backwards compatible. However, there were some significant changes prior to FF-A v1.3 because of SMCCC updates which added support for using more registers for argument passing and also the standardisation of the FF-A version renegotiation. To avoid adding complexity this crate implements the register usage convention as defined in FF-A v1.3, which might not be compatible with earlier versions.

Implemented features

• Supports converting FF-A interface types between Rust types and the FF-A register ABI.
• Memory transaction descriptor handling for FFA_MEM_* interfaces (partial).
• FF-A v1.1+ boot information protocol.
• FF-A partiton information descriptor.

Future plans

• Refactor FF-A descriptor versioning scheme and update all descriptor definitions to FF-A v1.3.
• Remove version argument for FF-A interface encoding/decoding (tentative).
• Implement missing interfaces and features of FF-A v1.3 and later.
• Increase test coverage.
• Create more detailed documentation to capture which parts of FF-A are currently supported.

License

The project is MIT and Apache-2.0 dual licensed, see LICENSE-APACHE and LICENSE-MIT.

Maintainers

arm-ffa is a trustedfirmware.org maintained project. All contributions are ultimately merged by the maintainers listed below.

• Bálint Dobszay balint.dobszay@arm.com balint-dobszay-arm
• Imre Kis imre.kis@arm.com imre-kis-arm
• Sandrine Afsa sandrine.afsa@arm.com sandrine-bailleux-arm

Contributing

Please follow the directions of the Trusted Firmware Processes

Contributions are handled through review.trustedfirmware.org.

Arm trademark notice

Arm is a registered trademark of Arm Limited (or its subsidiaries or affiliates).

This project uses some of the Arm product, service or technology trademarks, as listed in the Trademark List, in accordance with the Arm Trademark Use Guidelines.

Subsequent uses of these trademarks throughout this repository do not need to be prefixed with the Arm word trademark.

Copyright The arm-ffa Contributors.