IOMMU DMA-mapping API for arm64 ?

IOMMU DMA-mapping API for arm64 ?

[Will Deacon]

On Thu, Feb 06, 2014 at 05:05:45AM +0000, Ritesh Harjani wrote:
> Hi everyone,
> 
> I tried looking for IOMMU support in ARM64 but what I was able to see is
> only swiotlb is currently supported.
> 
> Based on my understanding for IOMMU support, we need DMA-MAPPING API to
> have IOMMU ops field, similar to what is present in arm32.  I could see
> the iommu field added in dev_archdata in below mentioned patch
> (arch/arm64/include/asm/device.h), but there is no ops field in
> arch/arm64/mm/dma-mapping.c ?

Correct, there needs to be a way to plumb dma-mapping into the IOMMU layer.

> I also saw one mail discussion between you guys on what is the best place
> for adding iommu support in ARM64, but couldn't see any followed up
> patches for the same.
> 
> Please tell us the current status/updates on the same. Your feedback will
> be greatly appreciated.

There are a few related topics here:

  (1) Moving a bunch of the boilerplate IOMMU code into a common place
      (iommu-helper.c or similar). This is because we don't want to blindly
      duplicate common code across architectures.

  (2) Standardising at least part of a system topology description in
      device-tree, so that we can deal with different combinations of
      {coherent,nocoherent} device {with,without} a series of IOMMUs.

Once both of those are sorted, the actual plumbing should be fairly
straightforward.

Will