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SubjectRe: Streaming DMA mapping question
On Fri, Sep 13, 2002 at 01:28:42PM -0700, David S. Miller wrote:
> From: Adam Kropelin <akropel1@rochester.rr.com>
> Date: Fri, 13 Sep 2002 16:21:50 -0400
>
> On Fri, Sep 13, 2002 at 12:36:41PM -0700, David S. Miller wrote:
> > Actually, rather it appears that the i386 pci_unmap_*() routines need
> > the write buffer flush as well.
>
> Ah, a bug then.
>
> On further discussion with Alan Cox, the bug is actually that
> pci_map_*() needs the write buffer flush added. pci_map_*()
> and pci_dma_sync_*() transfer ownership from CPU to PCI controller
> as abstracted in DMA-mapping.txt Therefore these are the cases
> where the CPU write buffers need to be flushed.

Makes sense to me.

> Really, the cases handled by the x86 write buffer fluses are very
> marginal and unlikely to happen. In fact the write buffer flush on
> x86 is done on winchip and ppro chips only.
>
> I think you're problems are elsewhere :-)

Probably true, but the test machine I'm running on *is* SMP ppro ;)

--Adam

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