https://bugs.freedesktop.org/show_bug.cgi?id=100712
--- Comment #8 from Julien Isorce julien.isorce@gmail.com --- Hack submitted here https://patchwork.kernel.org/patch/9695945/. It contains some info in the commit message and in the replies. For those who want to try, it is easier to just set R600_DEBUG=nowc as said in #7.