[PATCH] MGA DDX: default to use EXA if XAA is unavailable

[Adam Jackson]

On Sun, 2015-06-21 at 19:55 +0200, Matthew Rezny wrote:
> The MGA DDX still defaults to XAA because the EXA support is buggy on some 
> hardware. Unfortunately, XAA support is gone from newer versions of the 
> xserver. If only EXA is present, that is usually better than no accel, so use 
> it by default. Patch to default to EXA when lacking XAA inspired by r128.

At this point the majority of Matrox G-series chips in the world are
G200e-based server chips, which don't have a working 3D engine and thus
basically can't do exa's Composite hook at all.  We should be falling
back to shadowfb not noaccel when there's neither exa nor xaa though.

However, hilariously, mga hasn't been mapping the framebuffer write
-combining since the pciaccess port.  If you saw a significant
performance improvement with this patch, I'd be curious to know how
this patch compares when using shadowfb:

http://cgit.freedesktop.org/xorg/driver/xf86-video-mga/commit/?id=04432b9c1db255e8e3d39a924f8803f83c407acc

- ajax