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

[Marek Olšák]

On Tue, Aug 9, 2016 at 3:47 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> 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?

I don't know.

How does this ensure that Mesa and ROCm addrlib copies won't diverge?

What issues can we expect if Mesa and ROCm addrlib copies diverge?

For texture sharing, the buffer metadata is set in a way that doesn't
leave any room for interpretation. I think it's possible to bypass
addrlib in this case.

Marek