For some chipsets (Intel HD 4000 / Ivy Bridge) mesa's DRI3 support is still lacking: for example, resolution changes are simply not seen by OpenGL applications. This is nothing specific to modesetting as it affects the intel driver as well (see https://bugs.freedesktop.org/show_bug.cgi?id=97916). HOWEVER The intel driver allows disabling DRI3 by adding Option "DRI" "2" in xorg.conf. To my knowledge, the modesetting driver has no such option, and the only way to disable DRI3 is to rebuild xorg with --disable-dri3. On distros that enable DRI3 by default, it's inconvenient to rebuild xorg after each update. Would it be difficult to add a similar Option "DRI" to the modesetting driver?
FWIW, DRI3 can be disabled on the client side for OpenGL apps via the environment variable LIBGL_DRI3_DISABLE=1.
Aha, that's what I was looking for, thanks! I added export LIBGL_DRI3_DISABLE=1 to my login script and it does the job nicely. No need to add a configuration option then. I'll close this request.
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