[OpenBIOS] Reducing OpenBIOS memory footprint

[Tarl Neustaedter]

On 2010-12-2 6:21 AM, Mark Cave-Ayland wrote:
> [...]
> This seems to suggest memory within the 0xff rather than the 0xfe range. 
> Interestingly enough, the screen device looks like this:
>
> screen:  '/iommu at 0,10000000/sbus at 0,10001000/cgsix at 3,0'
>
> Perhaps it's hiding on the SBUS and so it doesn't need a direct mapping? 
> Does the IOMMU allow paged access into SBUS space to avoid having to map it 
> in its entirety?

Not sure I understand your question - but yes, the IOMMU (IO memory management 
unit) allows paged access into SBUS space. When "map-in" is called, it maps 
only the specific pages into virtual memory without bringing the rest of SBUS 
in. We do the same on PCI without having a separate iommu node.

I'll admit that SBUS is at the very edge of my knowledge - my first project at 
Sun was PCI for SPARC (1994), so SBUS was already on its way out.