12 display, two card single desktop without Xinerama

[Austin Godber]

Hi All,

I have an Ubuntu 12.0.4 machine with two ATI FirePro V9800 and 12 Dell
DisplayPort Displays attached.  I can get all of that merged into a single
7680x6400 desktop if I use Xinerama, but I've been unable to figure out how
to extend the desktop beyond a single card with 6 displays just using
Xrandr.  The attached xorg.conf works with just a single card ... my
attempts to expand it to the second card have failed.  I've been able to
display on one card or another by specifying specific "Devices" (with the
appropriate BusIDs), but never both at once.

Is it possible for a single Screen to include two Devices?  It just seemed
to use the last specified if I tried it.

X Version:
X.Org X Server 1.11.3

Driver:
[ 12862.289] (II) Module fglrx: vendor="FireGL - AMD Technologies Inc."
[ 12862.289]    compiled for 1.4.99.906, module version = 12.10.5
[ 12862.289]    Module class: X.Org Video Driver

LSPCI Output:
02:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Cypress XT [FirePro V9800]
07:01.0 VGA compatible controller: Matrox Electronics Systems Ltd. MGA
G200eW WPCM450 (rev 0a)
83:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Cypress XT [FirePro V9800]

I specifically want to avoid Xinerama so that Xrandr works so I can
dynamically resize the desktop resolution to accommodate both a high and
low resolution mode.

Thanks for any input you have,

- Austin
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