Removing direct graphics access from DGA

[Mark Kettenis]

> From: Keith Packard <keithp at aiko.keithp.com>
> Date: Sun, 20 Sep 2009 14:00:50 -0700
> 
> Yes, I've seen DGA work, and it could be made to work again on at
> least some of our hardware. However, it's been broken for any driver
> exposing RandR 1.2, and the last bug report about this was from
> 2007. Either people have given up hoping to see this fixed or they
> just aren't using it anymore.
> 
> In any case, the mmap API can't be exposed reliably for resizeable
> frame buffers as there's no way to revoke a mapping.

There's a fairly simple solution for that though: don't allow RandR to
resize the framebuffer if it is mapped through DGA.