[knc1]

Was gumstick using the mainline kernel?

For a long time, ARM was maintained outside of the mainline kernel repository, in a repository of its own.
AND
The changes where very slow to be pushed to Linus.
(It became a rather 'hot' issue before the workflow among the groups was resolved.)

You will notice the same with the Freescale kernel (in its company repository) vs. the mainline kernel.

Note:
A lot of this "interesting" history was lost when mainline was re-built after kernel.org got hacked.
But perhaps it can be found in the various (original) manufacturers repositories and/or 'network wayback' sites might have copies of "before the hack" mainline repositories.