Page MenuHomePhabricator

Project Maintenance Process
Updated 1,303 Days AgoPublic

Goal of this document

As the developers community at is growing, there is an increasing need to have work processes that are clearly documented, feel smooth and scale well. The aim of this document is to define a set of rules, guidelines and processes to try and improve the way we work together as a community today. In particular, some of these goals are:

  • To make the code review process more explicit and clearly documented.
  • To set expectations for contributors and reviewers.
  • To establish a hierarchy of roles and their responsibilities.
  • To provide guidelines for new contributors.
  • To enlarge maintainership to developers outside of Arm.

We hope that it will make it easier for people to contribute to the projects, improve the time it takes to get patches merged in the tree, make the process more transparent, while reducing potential frictions and frustration that can arise in the community.

This document applies to the TF-A and TF-M projects right now but might be extended to other projects in the future.

Definitions of roles, rights and responsibilities

There are several roles that people contributing to the project can assume. Different roles come with different rights and responsibilities and are attributed based on the level of expertise and engagement in the project, the bandwidth, to name a few.


Default role for anyone starting to contribute to the project.

Contributors can:

  • Submit patches for review with an aim to get them merged upstream.
  • Review other people's patches. Although their valuable input is always welcome, it is not sufficient to get a patch approved and merged. Similarly, they can express concerns but these cannot veto a patch. See section "Life Cycle of a Patch - From submission to integration in the tree" below.
  • Participate on the development mailing list.

Code Owner

Someone who looks after a particular module of the source tree (for example: the power management layer or a specific platform port.)

The project keeps a list of code owners, their contact information along with the modules they manage. Ideally, every module in the code base should have a dedicated code owner, as orphan modules are likely to break over time.

Code owners will get requested to review patches in the modules they own and they are responsible to do so in a timely manner. If several code owners are looking after the same module, each patch needs only approving by one of them (but more of them might do it if they wish). A code owner shall have a genuine interest in the said module and have enough bandwidth to deal with incoming reviews and general design discussions.


There are a number of maintainers assigned to the project. The project keeps a list of them along with their contact information. Maintainers don't necessarily need a deep domain expertise of all areas of the project, instead they look at the project from a high level perspective. They are expected to ensure that changes adhere to the project's quality criteria, to its architectural direction, to its threat model and so on.

Code owners and maintainers are complementary roles.

Unlike code owners, maintainers can approve any patch, no matter what module it concerns. They are responsible for ensuring patches have had enough overall review and adding their own approval in a timely manner.

They also have merge rights, i.e. the ability to merge a patch in the tree once it has received all required approvals.

Note that roles can be cumulative, in particular the same individual can be both a code owner and a maintainer.

How to become a code owner?

Usually, the individual contributing a new major piece of code to the project naturally becomes the code owner for this module. Such a major contribution is expected to be accompanied by an update to the list of code owners.

It is strongly frowned upon to contribute a major piece of code and not nominate yourself (or someone you know and work with) as the code owner for it, as then there is no one to look after this module with the right expertise.

For existing code that already has a code owner (or several), if you wish to help and become an additional code owner for this module, you may propose your candidature. To do this, add yourself to the list of code owners and submit the resulting patch for review, adding all other code owners for this module as reviewers. At least 2 existing code owners (or 1 if there is a sole code owner) must approve it and none of them must veto it.

How to become a maintainer?

Maintainers are elected by their peers on a meritocracy basis.

To be assigned as a maintainer, you need to satisfy the criteria set by the project. This typically covers things like:

  • Being an active member of the project for a minimum duration.
  • Having contributed a substantial number of non-trivial and high-quality patches


  • Having reviewed a substantial number of non-trivial patches, preferably in the generic layer, with high-quality constructive feedback.
  • Behaving in a professional and polite way, with the best interests of the project at heart.
  • Showing a strong will to improve the project and to do the right thing, rather than going for the quick and easy path.
  • Participating in design discussions on the development mailing list.
  • Having appropriate bandwidth to deal with the workload.

Life Cycle of a Patch - From submission to integration in the tree

All the above roles play a part in the life cycle of a patch. This section outlines who needs to do what in order for a patch to be approved and merged.

When posting a new patch for review, a contributor (and patch author) must choose his reviewers. A patch must be approved by:

  • At least 1 code owner for each module modified by the patch.
  • At least 1 maintainer.

Thus the patch author should put as reviewers the right people to reach this target. They may add more, and they may also add some non-code owners if they think they might provide useful input (because of their past work and experience for example). Appropriate code owners might be found by looking at the list of code owners for the project. Similarly for maintainers. For additional non-code owners, it is also useful to run a "git blame" on the source code to find out who's been recently working on this area of the code.

The patch author is responsible for addressing all review comments from all code owners and maintainers, until they approve the patch.

Addressing a comment might mean 2 things, depending on the nature of the comment:

  • Questions are addressed by providing an answer.
  • Suggestions can be addressed in one of 3 ways:
    • Adopt it immediately and post the reworked version.
    • Defer it to a subsequent change. The patch author is then responsible for making sure it gets done at some point in the future.
    • Disagree and provide additional info to explain your approach.

Once a patch has been approved by all relevant code owners and maintainers, it can be merged.

In case of disagreement between the different parties involved in the review, leading to a stalemate situation where the patch cannot progress further, a third-party maintainer should be called out to settle the case.

It is important to note that the patch author is responsible for driving his review. In particular, they should not expect that people will review their patches if they don't request them to do so. On the other hand, once someone has been asked to review a patch, they should do so in a timely manner, or if they don't have the bandwidth to do it at this moment in time, they should say it explicitly. In this case, the patch author should look for another appropriate reviewer.

Patch Contribution Guidelines

Here are some general guidelines all patches are expected to comply with.

  • Keep patches small, split them in logical units. Keep them on topic ; if you need to fix another bug or make another enhancement, please push them into a separate patch.
  • Write informative and comprehensive commit messages. A good commit message provides all the background information needed for reviewers to understand the intent and rationale of the patch. This information is also useful for future reference.
  • The patch compiles without any warnings for all supported configurations.
  • The patch meets the project's code quality criteria.
  • The patch adheres to the project's coding style.
  • The documentation has been updated accordingly.
  • The continuous integration (CI) system has been updated accordingly (or will shortly be after the code updates).
  • The patch has been tested as per the testing requirements of the project. In particular, it passes all CI tests, does not introduce any regression and does not break existing code. In the case where the required tests have not been integrated in the CI just yet, additional targeted testing has been locally conducted and details of that (list of tests and results) have been made available.

These apply as much to generic code as to platform code.

These general guidelines might be extended or refined by projects.

Platform Support Life Cycle

Maintaining a platform essentially consists in keeping up to date the following items:

  • Documentation.

Platform documentation should typically describe the hardware, what features in the project are supported on this platform, how they are configured and how to use them.

  • Build support.

All supported configurations should build cleanly.

  • Continuous integration (CI) system.

Proper testing for this platform should be deployed in the CI and maintained over time.

This is a lot of work and it would be unreasonable to expect that in an open source project all platforms are supported forever. The following stages of a platform's life cycle are defined as a way of managing that.

Fully Supported

A fully supported platform needs to meet the following requirements:

  • It builds with all the versions of toolchains supported by this platform.
  • It builds all the configurations supported by this platform.
  • All supported configurations are tested in the CI and all tests pass.
  • The documentation is up to date (in particular the list of supported features).

Note that it is acceptable for some of these items to be temporarily broken or out of date, so long as they are clearly tracked by tickets.

Limited Support

The platform is supported to some degree but not every criteria of a "fully supported" platform is satisfied. For example, some build configurations fail, or some tests fail, or the platform does not have a fully functional, complete CI loop just yet.

The documentation should still clearly state what's known to work and what's broken.

What does not work will be disabled in the CI to keep it healthy and useful to everyone.

This is intended as a temporary state until the platform can be brought back into "fully supported" state. If the situation does not improve, it will become "deprecated" after some time.


The platform is no longer supported. It could be because it has reached its end of life or there is a lack of interest in the community.

Deprecated platforms may be removed from the codebase in future.

Per-project guidelines

This document outlines the general expectations for all projects. In most cases, projects would typically extend and/or refine these in a complementary document.

Such project guidelines would typically cover the following range of topics (this list is not exhaustive):

  • Code review timelines (Defining "All patches to be reviewed in a timely manner").
  • Code review guidelines.
  • Documentation guidelines.
  • Testing standards.
  • Code of conduct. Among other things, this would define a way to measure maintainers and code owners inactivity and how to give them notice that their roles might be revised if they don't resurface, or warn them about impending life cycle state changes.
  • Deprecated platforms policy (e.g. keep them forever in the tree for reference, remove them after some time, ...)
  • Process to document the list of features in the project and their level of support for each platform.
  • Define standard labels for the ticketing system (per platform/feature/version/...).
  • Branching strategies.

Exclusions and complementary notes

There are things we thought about but did not include in this document on purpose. These are listed below for completeness.

  • We will most likely need a deviation to the code review process for patches that need to be fast-tracked. This should only apply in some circumstances and will depend on the nature of the patch.
  • In the future, we'll most likely need to organize "key signing" type of events to enforce the legitimacy of maintainers and code owners to the tools, i.e. to prove that they really are who they claim to be and protect our tree from user identity spoofing.
  • The list of code owners and maintainers for the project might be provided in a file in the source tree. A common file for both is likely to be the more convenient solution. In the future, it might be worth developing some tools (or reusing existing ones if the license is compatible) to assist developers (for example suggesting specific code owners or maintainers based on the nature of the patch).
  • For both TF-A and TF-M, the CI system is not quite ready to be extended by the community. Thus, some of the guidelines around adding the required level of testing in the CI cannot be applied right now. We hope the situation will quickly evolve, which is why it's been included in this document nonetheless.
  • In the future this document might be expanded to address multi-branch maintainership.

Versions and history

1.011/05/2020First version.
Last Author
Last Edited
May 11 2020, 7:45 AM