IOMMU DMA-mapping API for arm64 ?

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