On Fri, Apr 01, 2005 at 11:22:21AM +0200, Bas Wijnen wrote: > Hi, > > I'm not very familiar with DMA, but I remembered that only certain pages > can be used for DMA. Or was that only for ISA? Anyway, if that is not > the case, it becomes a lot simpler. >
It's true for ISA but also for PCI in some 64bit systems. In general we
have the following magic barriers on IA32/AMD64 systems :
1MB : 8bit ISA DMA
16MB : 16bit ISA DMA
4GB : Non-DAC capable PCI cards on 64bit systems lacking an IO-MMU.
(DAC stands for Dual Address Cycle here. Ie. the ability to use a
64bit address by doing two 32bit address cycles).
Additionally 8 and 16bit ISA DMA transfers can't cross a 64KB or a 128KB
boundary respectively.
Cheers,
Peter (p2).
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