[Mesa-dev] Moving amdgpu/addrlib into a git submodule

[Nicolai Hähnle]

Hi everybody,

addrlib is the addressing and alignment calculator which is used by 
radeonsi. It's developed (and also used) internally at AMD, and so far 
we've had one open source copy living in the Mesa repository at 
src/gallium/winsys/amdgpu/drm/addrlib.

The question of using addrlib in non-Mesa parts of our open-source stack 
has come up, in particular in relation to compute. We'd obviously like 
to share the code rather than having multiple copies flying around. 
Since the interface of addrlib is slow-moving but unstable, shared 
linking is not an option.

I think the best way forward is to create a dedicated repository for 
addrlib which is then integrated into Mesa as a git submodule.

The point of this email is to gather feedback from the Mesa community on 
this plan, which is explicitly:

(0) Create an addrlib repository, say amd/addrlib on fd.o.
(1) Add it as a git submodule to the Mesa repository.
(2) Fix up whatever aspects of the build system that may be affected 
(perhaps for building source tarballs).
(3) Go back to mostly ignoring addrlib, except for trying to get better 
at syncing with the internal closed-source version.

 From initial experiments, the impact on users interested in radeon is 
that they will have to run `git submodule init` and then occasionally 
`git submodule update`. Users who do not build radeonsi should be able 
to ignore the change completely.

There are alternatives. For example, ROCm uses Google's repo tool 
already. But for Mesa, git submodule looks like a lightweight, well 
supported and overall conservative option that everybody should already 
have installed. If there are good arguments for something else, let's 
hear them!

Another point: if we proceed with this plan, I think we should consider 
moving addrlib into src/amd/addrlib. There are two reasons: First, 
transitioning to a submodule *without* changing the directory is 
probably more fragile, i.e. what happens when you switch between 
checkouts before and after the transition. Second, if/when radv ends up 
being merged into Mesa master, it makes sense to have addrlib there anyway.

Thoughts? Complaints? Praise?
Nicolai