[ofa-general] iommu dma mapping alignment requirements

[Steve Wise]

Benjamin Herrenschmidt wrote:
> On Thu, 2007-12-20 at 13:29 -0600, Steve Wise wrote:
> 
>> Or based on the alignment of vaddr actually...
> 
> The later wouldn't be realistic. What I think might be necessay, though
> it would definitely cause us problems with running out of iommu space
> (which is the reason we did the switch down to 4K), is to provide
> alignment to the real page size, and alignement to the allocation order
> for dma_map_consistent.
> 
> It might be possible to -tweak- and only provide alignment to the page
> size for allocations that are larger than IOMMU_PAGE_SIZE. That would
> solve the problem with small network packets eating up too much iommu
> space though.
> 
> What do you think ?

That might work.

If you gimme a patch, i'll try it out!

Steve.