If I'm following the conversation correctly, it doesn't break anything, the kernel developers don't understand it. Also, the followup from Alex Deucher of the AMD team is interesting: https://lists.freedesktop.org/archives/dri-devel/2016-Decemb... Basically, he reckons that the atomic modesetting code is a poorly-thought out and maintained disaster that regularly breaks multiple drivers - and having somewhat followed the changelogs, I can entirely believe this. (Dave Airlie responds by blaming AMD for not sufficiently testing the upstream kernel developers' buggy changes to their drivers.)