[Intel-gfx] [PATCH 1/6] lib/scatterlist: add sg_set_dma_addr() function

[Christoph Hellwig]

On Mon, Mar 16, 2020 at 10:41:42AM +0100, Christian König wrote:
> Well I would prefer if the drivers can somehow express their requirements
> and get IOVA structures already in the form they need.
> 
> Converting the IOVA data from one form to another is sometimes quite costly.
> Especially when it is only temporarily needed.

We basically have two ways to generate the IOVA:

  - a linear translation for the direct mapping case or some dumb IOMMU
    drivers - in that case case there is a 1:1 mapping between input
    segments and output segments in DMA mapping
  - a non-trivial IOMMU where all aligned segments are merged into
    a single IOVA range

So I don't really see how the dma layer could help much with any
limitation beyond existing max size and dma boundary ones.