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SubjectRe: Kernel virtual memory?
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davem@jenolan.rutgers.edu said:
> On Sparc all DMA on SBUS is based on virtual addresses. Each SBUS
> has a dedicated "IOMMU" tlb which performs the va-->pa translations.

If I recall, that only applies to a small region in lower memory. You
are talking about vdma and I believe it was only the low meg or something
silly.

Not ALL dma uses the vdma, just the DMA addresses within the vdma region.
Furthermore, there is a single IOMMU for all the devices on the SBus,
getting you right back to the precious resource problem.

(Way back when I was involved with writing a SunOS driver for a board
my cousin built, that did direct video to a printer. I think we concluded
that scatter-gather was more practical.)
--
Steve Williams
steve@icarus.com
steve@picturel.com

"The woods are lovely, dark and deep. But I have promises to keep,
And lines to code before I sleep, And lines to code before I sleep."



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