On 01/10/17 10:02, Christoph Hellwig wrote:
> Hi all,
>
> are there any road blocks for using drivers/iommu/dma-iommu.c for more
> than just arm64, e.g. also for the Intel/AMD iommus? I've been trying
> to consolidate the giant amounts of duplicate code in the dma ops
> implementations for a while, and iommus that provide an iommu_api
> driver seems like an easy enough target. I remember we had discussions
> about such things a while ago, so I wonder if its just that no one got
> to this yet or if there are any known issues that need to be solved
> first.
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.
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.
Robin.
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