Comment # 8 on bug 89536 from Michel Dänzer

(In reply to Rafael Ristovski from comment #7)
> I just downgraded, PRIME worked flawlessly up until 3.19, I was able to test
> up until 3.17.6-1 since the next one after that was the latest kernel in the
> [testing] repo aka 3.19.2-1

Can you narrow it down further, ideally bisect?