On Wednesday 19 September 2012, Hiroshi Doyu wrote:

I guess that it would work. Originally I thought that using DMA-API
and IOMMU-API together in driver might be kind of layering violation
since IOMMU-API itself is used in DMA-API. Only DMA-API used in driver
might be cleaner. Considering that DMA API traditionally handling
anonymous {bus,iova} address only, introducing the concept of
specific address in DMA API may not be so encouraged, though.

It would be nice to listen how other SoCs have solved similar needs.

In general, I would recommend using only the IOMMU API when you have a device
driver that needs to control the bus virtual address space and that manages
a device that resides in its own IOMMU context. I would recommend using
only the dma-mapping API when you have a device that lives in a shared
bus virtual address space with other devices, and then never ask for
a specific bus virtual address.

Can you explain what devices you see that don't fit in one of those two
categories?

	Arnd