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SubjectRe: Define CONFIG_BOUNCE to avoid useless inclusion of bounce buffer logic.
Christoph Lameter writes:

> > The DMA zone is for memory allocations _for_ _DMA_. If all your memory
> > is DMA-able then it belongs in the DMA zone.
> Nope. The DMA zone is for crappy DMA devices that can only use a portion
> of memory.

That is (presumably) true today, but is in fact a redefinition of what
ZONE_DMA historically was for.

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.

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