https://bugs.freedesktop.org/show_bug.cgi?id=66551
--- Comment #1 from octoploid octoploid@yandex.com --- OK, I've just double checked and the issue doesn't depend on DPM being enabled. A vanilla Linus kernel (latest git) with DPM disabled will also hang.
I'm using:
x11-drivers/xf86-video-ati-7.1.0 media-libs/mesa-9.1.4 x11-libs/libdrm-2.4.46
Any idea on how to further debug this issue?