Phyr Starter

[Keith Busch]

On Thu, Jan 20, 2022 at 02:56:02PM +0100, Christoph Hellwig wrote:
>  - on the input side to dma mapping the bio_vecs (or phyrs) are chained
>    as bios or whatever the containing structure is.  These already exist
>    and have infrastructure at least in the block layer
>  - on the output side I plan for two options:
> 
> 	1) we have a sane IOMMU and everyting will be coalesced into a
> 	   single dma_range.  This requires setting the block layer
> 	   merge boundary to match the IOMMU page size, but that is
> 	   a very good thing to do anyway.

It doesn't look like IOMMU page sizes are exported, or even necessarily
consistently sized on at least one arch (power).