I have a Linux machine running Ubuntu 12.04LTS. It has a Phenom II 940 processor, and a Gigabyte AM2+ motherboard with integrated HD3200 graphics. Machine was new in 2009.
It is currently set up as a dual monitor setup (one off the DVI port, one off the VGA port) and everything just works. Transparent windows, compositing, accelerated 3D, seamless transition between the two monitors (even though they are different resolutions) - everything is fine.
I did this by downloading the driver shell script based installer direct from AMD and running that (so I'm not using a Ubuntu repository for the drivers). This is mildly annoying in that every time Ubuntu bumps the kernel version, graphics breaks on reboot until I re-run the installer and reboot again, but that's a minor issue.
With the release of Steam, I tried playing Portal on this rig, and it works - barely. Frame rate at the 1080p resolution of the primary monitor dives whenever the camera can see into a portal, and that limits playability. As a proof-of-concept, it's very exciting, but it is clear that the HD3200 is tapped out.
In addition, AMD support for the 3200 has been pulled out of the regular drivers and has transitioned to the Legacy drivers, which has me nervous about being able to respond to future kernel updates should the driver API change.
So to counter that, I bought an Asus HD7870 card that I will be installing this weekend.
Reading through the motherboard documentation in preparation for the upgrade, I discovered that there is, in theory, potential to run the onboard graphics concurrent with the PCIe card, in a mode called "Hybrid Crossfire". I can't imagine this adding a whole lot of extra performance, given the raw horsepower differential between the two graphics processors, but at some point I will be adding a third monitor to this system and it would be great to have the 3200 drive this monitor (alternatively, I may want to drive a TV off the HDMI port - video only, not gaming - and the 3200 might be a good way to do that)
So then, here are my questions:
1. Can the drivers for the modern card and Legacy drivers for the onboard graphics co-exist on the same system? How would this work?
2. Assuming #1 is possible, can this make use of Hybrid Crossfire? Is it even worth doing?
3. Assuming #1 is not possible using the Catalyst drivers, how about using Catalyst to drive the 7870 and using the open source drivers to power the 3200? What would be the limitations of such a setup?