iommu sg merging: swiotlb: respect the segment boundary limits

iommu sg merging: swiotlb: respect the segment boundary limits

This patch makes swiotlb not allocate a memory area spanning LLD's segment
boundary.

is_span_boundary() judges whether a memory area spans LLD's segment boundary.
If map_single finds such a area, map_single tries to find the next available
memory area.

Signed-off-by: FUJITA Tomonori <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Greg KH <[email protected]>
Cc: Jeff Garzik <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>