There is many ways how to manage the growing delta between the some current kernel API and the API of an older, distro specific kernel.
This page collects the specific issues, how different people deal with them and from there we come up with some best practices how to do it with least effort.
As we anticiapte distro differences in the kernel even once we have these best practices, this page also lists the distro specifics of the kernels.
So in one sentence the scope of this effort is
- how to systematically backport upstream drivers to distro kernels
- which kernel is on which distro?
- updated subsystems from later kernels?
how is it done?
However the different target kernels are managed and the API backports may be shared, we need a common Driver backport exchange format  to share backported drivers between vendors in source format.