From mboxrd@z Thu Jan  1 00:00:00 1970
From: Grant Grundler <grundler@cup.hp.com>
Date: Thu, 17 Oct 2002 22:10:13 +0000
Subject: Re: [Linux-ia64] BitKeeper tree for 2.4.x
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To: linux-ia64@vger.kernel.org

Steffen Persvold wrote:
> Kinda complicated though... I thought the IO system didn't use coherence
> protocols, and it was because of that we needed API functions such as
> pci_dma_sync_single() and pci_dma_sync_sg() to manually ensure coherence..

The original problem was some IOMMU's can not support a static translation
for all physical memory - ie virt_to_bus() wouldn't work.
"manual coherence" works because the design accomodates SW IOTLB
("bounce buffers") model.

Supported HP PARISC and IA64 IOMMU's participate in the coherency protocol.

grant