- pci_map_sg/dma_map_sg are used with a scatter gather list that doesn't
  come from the block layer (e.g.  some network drivers do).

- how IOMMUs merge adjacent elements of the scatter/gather list is
  independent of how the block layer determines sees elements.
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>