Comment 4 for bug 715939

I suspect that what's actually happening here is that, when ForceGallium is enabled, mesa isn't loading the dri module - because ForceGallium causes mesa to look for r600g_dri.so rather than r600_dri.so.

Does copying r600_dri.so to r600g_dri.so in your mesa build fix things? That's what we do in the Ubuntu mesa build - copy the gallium driver to r600g_dri.so so we can install both r600c and r600g.