I ran openSUSE Tumbleweed (kernel 3.14.2 64bit), Mesa 10.1, llvm 3.4, on radeonSI / HD 7950 card, it worked nicely ... until update to Mesa 10.2rc1 with xserver 1.15.99 (latter needed because it now bundles updated glamor for 2d accel).

Working openGL apps:

• KDE compositing,
• google-earth
• teeworlds (game)
• video accel (vlc and xbmc 12.3 with vaapi)

Doesn´t work:

• steam (window completely distorted)
  

Error message:

• OpenGL GLX context is not using direct rendering, which may cause performance problems. For more information visit https://support.steampowered.com/kb_article.php?ref=9938-EYZB-7457.

Suggested solutions tried, which did not help

• adding user to video group (was already in place)
• checking 32bit mesa dependencies (everything in place)

strange:
glxinfo | grep direct
libGL error: dlopen /usr/lib/dri/updates/radeonsi_dri.so failed (/usr/lib/dri/updates/radeonsi_dri.so: cannot open shared object file: No such file or directory)
ATTENTION: default value of option force_s3tc_enable overridden by environment.
direct rendering: Yes

further diagnostics:

• dmesg: https://gist.github.com/tomtomme/a249f3ba95a9db6bb46b
• glxinfo: https://gist.github.com/tomtomme/5d95fdd4d9a906694846
• steam output on terminal: https://gist.github.com/tomtomme/ec8dfe72cf5eba0dc669