On Mon, Feb 22, 2016 at 11:15:09AM -0800, Doug Anderson wrote:

Note that historically I remember that Linus Torvalds has stated that
there is no stable API within the Linux kernel and that forcing the
in-kernel API to never change was bad for software development.  I
tracked down my memory and found
<http://lwn.net/1999/0211/a/lt-binary.html>.  Linus is rabid about not
breaking userspace, but in general there's no strong requirement to
never change the driver API inside the kernel.  That being said,
changing the driver API causes a lot of churn, so presumably changing
it in a backward compatible way (like adding to the API instead of
changing it) will make things happier.

You do need to fix the users though, change is fine but you can't cause
people's systems to break.