road blocks for using dma-iommu on more than arm64

[Christoph Hellwig]

On Mon, Oct 02, 2017 at 03:47:06PM +0100, Robin Murphy wrote:
> dma-iommu does require that the IOMMU driver allows iommu_{un,}map() to
> be called in atomic context, but last time I looked I think it was only
> the AMD driver that needs attention there. The main other concern, for
> x86 at least, was the performance overhead of the extra level of API
> abstraction and indirection. However, dma-iommu is now on a par with all
> the IOVA optimisations, and once we've got the new IOMMU API TLB
> maintenance calls implemented and hooked up, the difference will
> hopefully be small enough to make the conversion viable.

Thanks, that's good news.

> It's been on my to-do list for ages to convert 32-bit ARM over to
> dma-iommu as well - some of the blockers like DMA configuration order
> have now been resolved, but there are still some awkward dependencies
> between IOMMU and DRM drivers that I need to get a handle on.

Talking about arm32 - do you remember why it uses it's own dmabounce
subsystem instead of swiotlb?