Messages in this thread | | | Date | Thu, 13 Jul 2006 08:46:58 +0300 | From | Muli Ben-Yehuda <> | Subject | Re: [openib-general] Suggestions for how to remove bus_to_virt() |
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On Wed, Jul 12, 2006 at 05:40:13PM -0700, David Miller wrote: > From: Roland Dreier <rdreier@cisco.com> > Date: Wed, 12 Jul 2006 17:11:26 -0700 > > > A cleaner solution would be to make the dma_ API really use the device > > it's passed anyway, and allow drivers to override the standard PCI > > stuff nicely. But that would be major surgery, I guess. > > Clean but expensive, you should not force the rest of the kernel > to eat the cost of something you want to do when it's totally > unnecessary for most other users. > > For example, x86 never needs to do anything other than a direct > virt_to_phys translation to produce a DMA address, no matter what > bus the device is on. It's a single simple integer adjustment > that can be done inline in about 2 or 3 instructions at most.
It's possible that even x86 will support multiple IOMMUs in the future - for example, the Calgary IOMMU support we recently added to x86-64 could be modified to work on plain x86 as well.
I like the idea of a per-device DMA-API implementation, but only if it can be done in a way that is zero cost to the majority of the users of the API. We already have dynamic dma_ops on x86-64 to support nommu, swiotlb, gart and Calgary cleanly, extending it to use a per-device dma-ops isn't too difficult.
Cheers, Muli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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