The bcache tree is rebased on Linus's tree every now and then.
Generally there is a bunch of branches that refer to the relevant
releases/backports of the bcache code.
Linus's tags are still intact though so you can do a git diff <tagname> or any
other <refspec>

For 3.2 it would be something along the lines of this:

git clone http://evilpiepirate.org/git/linux-bcache.git
git checkout bcache-3.2
git diff v3.2

Is the bcache-3.2 branch as up to date (wrt bcache code) as the bcache branch?

Thanks

James