I also see in apitrace that GLXChooseVisual returns with NULL when I to run
glxgears.
I also see in apitrace that GLXChooseVisual returns with NULL when I to run
glxgears.
An updated patch is now available from:

https://lists.freedesktop.org/archives/mesa-dev/2016-April/114409.html

As mentioned over here:

https://lists.freedesktop.org/archives/mesa-dev/2016-April/114412.html

we'are actively looking forward for feedback.

I've also attached the patch directly to this bug tracker for convenience:
r300g_be.patch