On Tue, Apr 12, 2005 at 12:18:15PM +0100, Maciej W. Rozycki wrote:
> > > I've been experimenting with trying various PCI cards I have lying
> > > around in my Origin 200, to see if I can make any of them work.
> > The current Linux implementation limits IP27 to cards with 64-bit
> > addressing capability.
> Do we have a problem with our implementation of PCI DMA masks or is the
> low 4GB of PCI address space already consumed on this system? The problem
> is most 32-bit PCI cards unfortunately do not support DAC.
32-bit devices can only address a tiny fraction of the address space on
IP27. To make matters more interesting, there is no memory at all in the
low 4GB of the crosstalk address space, so 32-bit PCI has to rely on the
yet non-existing support for the IOMMU. SGI trying to save a little too
much money on the external SRAM for the IOMMU in the Origin 200 finally
made it a hard to use in an OS, deadlock prone thing.