I fired up a Raspberry Pi 2 this afternoon and proceeded to update Raspbian, the Debian-based Linux distribution for the Raspberry Pi models. As mentioned in that earlier posting, this experimental OpenGL support is only working on the Raspberry Pi 2 currently and not the Pi Zero or original Pi.
The experimental OpenGL driver stack can be toggled via raspi-config from the advanced options.
After enabling the option and rebooting the Raspberry Pi 2, the OpenGL driver was indeed working!
OpenGL 2.1 support is exposed via this VC4 Gallium3D driver and the Raspbian release is currently based on Mesa 11.1.
I had plans to run some basic OpenGL benchmarks on the Raspberry Pi 2 driver with VC4, but sadly those plans so far were foiled. The Raspberry Pi 2 driver stack couldn't handle running the ARMv7 GFXbench and the other basic OpenGL ARM tests I tried with our benchmarking software also failed. So back to investigating those issues when time allows, but then again for ARM OpenGL performance I'd much rather be playing with the Jetson development boards... At least though the Raspberry Pi 2 now has faster glxgears!