[coreboot] how to prevent legacy resource conflict with multiple VGA cards

Myles Watson mylesgw at gmail.com
Thu Oct 28 19:35:21 CEST 2010

> 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.

> 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.


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