[RFC 0/2] ARM: DMA-mapping & IOMMU integration

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

Folloing the discussion about the driver for IOMMU controller for
Samsung Exynos4 platform and Arnd's suggestions I've decided to start
working on redesign of dma-mapping implementation for ARM architecture.
The goal is to add support for IOMMU in the way preffered by the
community :)

Some of the ideas about merging dma-mapping api and iommu api comes from
the following threads:
http://www.spinics.net/lists/linux-media/msg31453.html
http://www.spinics.net/lists/arm-kernel/msg122552.html
http://www.spinics.net/lists/arm-kernel/msg124416.html

They were also discussed on Linaro memory management meeting at UDS
(Budapest 9-12 May).

I've finaly managed to clean up a bit my works and present the initial,
very proof-of-concept version of patches that were ready just before
Linaro meeting.

What have been implemented: 

1. Introduced arm_dma_ops

dma_map_ops from include/linux/dma-mapping.h suffers from the following
limitations:
- lack of start address for sync operations
- lack of write-combine methods
- lack of mmap to user-space methods
- lack of map_single method

For the initial version I've decided to use custom arm_dma_ops.
Extending common interface will take time, until that I wanted to have
something already working.

dma_{alloc,free,mmap}_{coherent,writecombine} have been consolidated
into dma_{alloc,free,mmap}_attrib what have been suggested on Linaro
meeting. New attribute for WRITE_COMBINE memory have been introduced.

2. moved all inline ARM dma-mapping related operations to
arch/arm/mm/dma-mapping.c and put them as methods in generic arm_dma_ops
structure. The dma-mapping.c code deinitely needs cleanup, but this is
just a first step.

3. Added very initial IOMMU support. Right now it is limited only to
dma_alloc_attrib, dma_free_attrib and dma_mmap_attrib. It have been
tested with s5p-fimc driver on Samsung Exynos4 platform.

4. Adapted Samsung Exynos4 IOMUU driver to make use of the introduced
iommu_dma proposal.

This patch series contains only patches for common dma-mapping part.
There is also a patch that adds driver for Samsung IOMMU controller on
Exynos4 platform. All required patches are available on:

git://git.infradead.org/users/kmpark/linux-2.6-samsung dma-mapping branch

Git web interface:
http://git.infradead.org/users/kmpark/linux-2.6-samsung/shortlog/refs/heads/dma-mapping


Future:

1. Add all missing operations for IOMMU mappings (map_single/page/sg,
sync_*)

2. Move sync_* operations into separate function for better code sharing
between iommu and non-iommu dma-mapping code

3. Splitting out dma bounce code from non-bounce into separate set of
dma methods. Right now dma-bounce code is compiled conditionally and
spread over arch/arm/mm/dma-mapping.c and arch/arm/common/dmabounce.c.

4. Merging dma_map_single with dma_map_page. I haven't investigated
deeply why they have separate implementation on ARM. If this is a
requirement then dma_map_ops need to be extended with another method.

5. Fix dma_alloc to unmap from linear mapping.

6. Convert IO address space management code from gen-alloc to some
simpler bitmap based solution.

7. resolve issues that might araise during discussion & comments

Please note that this is very early version of patches, definitely NOT
intended for merging. I just wanted to make sure that the direction is
right and share the code with others that might want to cooperate on
dma-mapping improvements.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center



Patch summary:

Marek Szyprowski (2):
  ARM: Move dma related inlines into arm_dma_ops methods
  ARM: initial proof-of-concept IOMMU mapper for DMA-mapping

 arch/arm/Kconfig                   |    1 +
 arch/arm/include/asm/device.h      |    3 +
 arch/arm/include/asm/dma-iommu.h   |   30 ++
 arch/arm/include/asm/dma-mapping.h |  653 +++++++++++------------------
 arch/arm/mm/dma-mapping.c          |  817 +++++++++++++++++++++++++++++++++---
 arch/arm/mm/vmregion.h             |    2 +-
 include/linux/dma-attrs.h          |    1 +
 7 files changed, 1033 insertions(+), 474 deletions(-)
 create mode 100644 arch/arm/include/asm/dma-iommu.h

-- 
1.7.1.569.g6f426

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