$ DRI_PRIME=1 LIBGL_DEBUG=verbose glxinfo64
name of display: :0
libGL: OpenDriver: trying /usr/lib64/dri/tls/r600_dri.so
libGL: OpenDriver: trying /usr/lib64/dri/r600_dri.so
libGL: driver does not expose __driDriverGetExtensions_r600():
/usr/lib64/dri/r600_dri.so: undefined symbol: __driDriverGetExtensions_r600
libGL: Can't open configuration file /home/carasin/.drirc: No such file or
directory.
libGL: Can't open configuration file /home/carasin/.drirc: No such file or
directory.
display: :0  screen: 0
direct rendering: Yes
[snipped]

I think could be good if we will have implemented this func.

Found about the same funcs for intel:
http://cgit.freedesktop.org/mesa/mesa/commit/?id=1925a9aebd64b2e08574118891394d9d56db25ae