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DateThu, 24 May 2007 10:57:19 +0100
FromAlan Cox <>
SubjectRe: Define CONFIG_BOUNCE to avoid useless inclusion of bounce buffer logic.
> Also there is the problem that some drivers use ZONE_DMA allocations
> because their device can only generate addresses below some limit, but
> on a platform with an IOMMU there is in fact no restriction on what
> memory the device can access.Bzzzzzt - have to call your bluff on that one
The IOMMU mapping window itself may be out of range of some devices. This
is a big problem on AMD64 where the GART window is above the 2GB boundary
- you can do 64->32 nicely but 32->31/30/28/24, all of which turn up on
PC hardware, are no solved by the IOMMU only by GFP_DMA

Alan
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