[PATCH 11/12] swiotlb: move the SWIOTLB config symbol to lib/Kconfig

[Russell King - ARM Linux]

On Mon, Apr 23, 2018 at 07:04:18PM +0200, Christoph Hellwig wrote:
> This way we have one central definition of it, and user can select it as
> needed.  Note that we also add a second ARCH_HAS_SWIOTLB symbol to
> indicate the architecture supports swiotlb at all, so that we can still
> make the usage optional for a few architectures that want this feature
> to be user selectable.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>

Hmm, this looks like we end up with NEED_SG_DMA_LENGTH=y on ARM by
default, which probably isn't a good idea - ARM pre-dates the dma_length
parameter in scatterlists, and I don't think all code is guaranteed to
do the right thing if this is enabled.

For example, arch/arm/mach-rpc/dma.c doesn't use the dma_length
member of struct scatterlist.

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