[PATCH 1/5 v2] dma-mapping: add generic dma_get_page_shift API

[Christoph Hellwig]

Do we need a function here or can we just have a IOMMU_PAGE_SHIFT define
with an #ifndef in common code?

Also not all architectures use dma-mapping-common.h yet, so you either
need to update all of those as well, or just add the #ifndef directly
to linux/dma-mapping.h.