Re: raw I/O with device memory

Alan Cox (alan@lxorguk.ukuu.org.uk)
Fri, 7 May 1999 02:00:51 +0100 (BST)

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> > 1st) It does not work with memory located in a PCI device.
>
> Linux cannot perform IO on such memory right now. End of story. It
> will in the future: this is just one of a whole raft of related problems
> we have due to the backwards-compatible way virt_to_phys works.

You also need a blacklist of chipsets, and some work arounds. PCI-PCI DMA
is a gigantic can of worms. On some chipsets PCI->PCI DMA just doesnt happen
on others it locks up occasionally.

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