Hello linaro-dev,
One "stupid question" I've been having for a long time is why Google for Android tree management put up a "repo" tool instead of using git submodules. One reason why can think of is that git submodules weren't available in 2008, but I wondered if there're more history behind it.
Well, today, while researching repo's operation atomicity, I come up at some answers, which I'd like to share.
First, Google knows about git submodules of course, and that they would be pretty good for management of Android forest: http://code.google.com/p/git-repo/issues/detail?id=49 (that's 2009) and here's repo master branch commits it refers to: http://android.git.kernel.org/?p=tools/repo.git%3Ba=commit%3Bh=0125ae2fda18d...
Here's some discussion: https://groups.google.com/group/repo-discuss/browse_thread/thread/eeb8e32470...
It touches a lot of topics (like Gerrit's handling of cross-project changes), and after reading it I couldn't come up to some easy summary like "repo's moving towards switching to git submodules underneath", but that's at least some info.