One problem is that the in-box ATI driver for the UMA graphics is unstable.
Even with the factory BIOS?
So to get Win7 installed, I must add a PCI video card. When Win7 is installed with the PCI video card present, device manager reports that the UMA graphics device cannot find enough free resources.
When a reference BIOS is used, the device manager warnings are not present because the BIOS disables the UMA. One reference BIOS disables UMA only by clearing the PCI command register bits for memory and I/O decode. A different reference BIOS skips UMA initialization altogether. I think for now, the command register method might be easiest for coreboot.
OK
The problem with the existing coreboot CONFIG_CONSOLE_VGA_MULTI feature is that it can only disable graphics devices that are on an HT link. In the case of UMA, non-AMD or non-HT systems, it doesn't work.
I think the easiest thing to do would be to use the same mechanism to know whether or not to disable UMA. If there is another VGA card added, then the VGA bits will be set on bridges that aren't associated with UMA. The UMA device could check the tree for these bits and disable itself, or some more code could be added to generically do the same thing.
Thanks, Myles