https://bugs.freedesktop.org/show_bug.cgi?id=73053
--- Comment #25 from Juan Orti j.orti.alcaine@gmail.com --- (In reply to comment #24)
Does disabling hyperZ help? E.g., set env var R600_DEBUG=nohyperz in /etc/environment or however your distro handles global env vars.
With that variable set the behaviour is the same. I can log in KDE, but crash in a few minutes.