Messages in this thread |  | | Date | Thu, 04 Oct 2001 15:41:08 +0530 | From | "BALBIR SINGH" <> | Subject | Re: how to get virtual address from dma address |
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With Rik's reverse mapping patch, wouldn't we have the virtual address for the given physical address ? I have no clue about how the patch works, somebody willing to explain it?
Balbir
David S. Miller wrote:
> From: James Bottomley <James.Bottomley@HansenPartnership.com> > Date: Wed, 03 Oct 2001 17:44:18 -0500 > > (although I can see it may be expensive to walk iommu page tables) > >I know of hardware where doing the reverse mapping would not even be >possible, the page tables are in hardware registers and are "write >only". This means you can't even read the PTEs back, you'd have to >keep track of them in software and that is totally unacceptable >overhead when it won't even be used %99 of the time. > >The DMA API allows us to support such hardware cleanly and >efficiently, but once we add this feature which "everyone absolutely >needs" we have a problem with the above mentioned piece of hardware. > >Franks a lot, >David S. Miller >davem@redhat.com > >- >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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