David Brownell wrote:
> The BUG_ON at include/asm-generic/dma-mapping.h:19 is a
> bug in that "generic DMA" code ... and I've seen the
> same BUG reported from PPC folk too.

Something like this should be correct even on x86, but
there may be some cases where a platform_dma_supported()
is necessary.

IMO this needs an all-architectures patch.  Not many
will need a platform_dma_supported() ... but almost
every implementation of that simple call is broken.

- Dave