The VGA arbiter controls the PCI bus' routing of legacy VGA resources, specifically the video memory aperture at 0xa0000-0xb0000 (640k should be etc.) and a handful of I/O ports. Since 128k is far too small for a real framebuffer these days, every driver instead maps a linear version of VRAM through the PCI BAR. And no DRI2 drivers ever need I/O port access, because all operations they might be used for (legacy VGA CRTC setup, mostly) happen on the kernel side.
In other words, this just works, and we can stop breaking it.
Signed-off-by: Adam Jackson ajax@redhat.com