DMA-mapping framework redesign preparation - 请使用新的DMA API

"ARM DMA-Mapping Framework Redesign and IOMMU integration.pdf" 
mentioned in this article is here(good to read): 

/Files/super119/ARM-DMA-Mapping-Framework-Redesign-and-IOMMU-integration.pdf

Hello eveyone,



On Linaro Memory Management meeting in Budapest (May 2011) we have

discussed about the design of DMA mapping framework. We tried to

identify the drawbacks and limitations as well as to provide some a

solution for them. The discussion was mainly about ARM architecture, but

some of the conclusions need to be applied to cross-architecture code.



The first issue we identified is the fact that on some platform (again,

mainly ARM) there are several functions for allocating DMA buffers:

dma_alloc_coherent, dma_alloc_writecombine and dma_alloc_noncoherent

(not functional now). For each of them there is a match dma_free_*

function. This gives us quite a lot of functions in the public API and

complicates things when we need to have several different

implementations for different devices selected in runtime (if IOMMU

controller is available only for a few devices in the system). Also the

drivers which use less common variants are less portable because of the

lacks of dma_alloc_writecombine on other architectures.



The solution we found is to introduce a new public dma mapping functions

with additional attributes argument: dma_alloc_attrs and

dma_free_attrs(). This way all different kinds of architecture specific

buffer mappings can be hidden behind the attributes without the need of

creating several versions of dma_alloc_ function.



dma_alloc_coherent() can be wrapped on top of new dma_alloc_attrs() with

NULL attrs parameter. dma_alloc_writecombine and dma_alloc_noncoherent

can be implemented as a simple wrappers which sets attributes to

DMA_ATTRS_WRITECOMBINE or DMA_ATTRS_NON_CONSISTENT respectively. These

new attributes will be implemented only on the architectures that really

support them, the others will simply ignore them defaulting to the

dma_alloc_coherent equivalent.



The next step in dma mapping framework update is the introduction of

dma_mmap/dma_mmap_attrs() function. There are a number of drivers

(mainly V4L2 and ALSA) that only exports the DMA buffers to user space.

Creating a userspace mapping with correct page attributes is not an easy

task for the driver. Also the DMA-mapping framework is the only place

where the complete information about the allocated pages is available,

especially if the implementation uses IOMMU controller to provide a

contiguous buffer in DMA address space which is scattered in physical

memory space.



Usually these drivers don't touch the buffer data at all, so the mapping

in kernel virtual address space is not needed. We can introduce

DMA_ATTRIB_NO_KERNEL_MAPPING attribute which lets kernel to skip/ignore

creation of kernel virtual mapping. This way we can save previous

vmalloc area and simply some mapping operation on a few architectures.



This patch series is a preparation for the above changes in the public

dma mapping API. The main goal is to modify dma_map_ops structure and

let all users to use for implementation of the new public funtions.



The proof-of-concept patches for ARM architecture have been already

posted a few times and now they are working resonably well. They perform

conversion to dma_map_ops based implementation and add support for

generic IOMMU-based dma mapping implementation. To get them merged we

first need to get acceptance for the changes in the common,

cross-architecture structures. More information about these patches can

be found in the following threads:



http://www.spinics.net/lists/linux-mm/msg19856.html

http://www.spinics.net/lists/linux-mm/msg21241.html

http://lists.linaro.org/pipermail/linaro-mm-sig/2011-Sept...

http://lists.linaro.org/pipermail/linaro-mm-sig/2011-Sept...

http://www.spinics.net/lists/linux-mm/msg25490.html



The patches are prepared on top of Linux Kernel v3.2-rc6. I would

appreciate any comments and help with getting this patch series into

linux-next tree.



The idea apllied in this patch set have been also presented during the

Kernel Summit 2011 and ELC-E 2011 in Prague, in the presentation 'ARM

DMA-Mapping Framework Redesign and IOMMU integration'.



I'm really sorry if I missed any of the relevant architecture mailing

lists. I've did my best to include everyone. Feel free to forward this

patchset to all interested developers and maintainers. I've already feel

like a nasty spammer.



Best regards

Marek Szyprowski

Samsung Poland R&D Center





Patch summary:



Andrzej Pietrasiewicz (9):

  X86: adapt for dma_map_ops changes

  MIPS: adapt for dma_map_ops changes

  PowerPC: adapt for dma_map_ops changes

  IA64: adapt for dma_map_ops changes

  SPARC: adapt for dma_map_ops changes

  Alpha: adapt for dma_map_ops changes

  SH: adapt for dma_map_ops changes

  Microblaze: adapt for dma_map_ops changes

  Unicore32: adapt for dma_map_ops changes



Marek Szyprowski (5):

  common: dma-mapping: introduce alloc_attrs and free_attrs methods

  common: dma-mapping: remove old alloc_coherent and free_coherent

    methods

  common: dma-mapping: introduce mmap method

  common: DMA-mapping: add WRITE_COMBINE attribute

  common: DMA-mapping: add NON-CONSISTENT attribute



 Documentation/DMA-attributes.txt          |   19 +++++++++++++++++++

 arch/alpha/include/asm/dma-mapping.h      |   18 ++++++++++++------

 arch/alpha/kernel/pci-noop.c              |   10 ++++++----

 arch/alpha/kernel/pci_iommu.c             |   10 ++++++----

 arch/ia64/hp/common/sba_iommu.c           |   11 ++++++-----

 arch/ia64/include/asm/dma-mapping.h       |   18 ++++++++++++------

 arch/ia64/kernel/pci-swiotlb.c            |    9 +++++----

 arch/ia64/sn/pci/pci_dma.c                |    9 +++++----

 arch/microblaze/include/asm/dma-mapping.h |   18 ++++++++++++------

 arch/microblaze/kernel/dma.c              |   10 ++++++----

 arch/mips/include/asm/dma-mapping.h       |   18 ++++++++++++------

 arch/mips/mm/dma-default.c                |    8 ++++----

 arch/powerpc/include/asm/dma-mapping.h    |   24 ++++++++++++++++--------

 arch/powerpc/kernel/dma-iommu.c           |   10 ++++++----

 arch/powerpc/kernel/dma-swiotlb.c         |    4 ++--

 arch/powerpc/kernel/dma.c                 |   10 ++++++----

 arch/powerpc/kernel/ibmebus.c             |   10 ++++++----

 arch/powerpc/platforms/cell/iommu.c       |   16 +++++++++-------

 arch/powerpc/platforms/ps3/system-bus.c   |   13 +++++++------

 arch/sh/include/asm/dma-mapping.h         |   28 ++++++++++++++++++----------

 arch/sh/kernel/dma-nommu.c                |    4 ++--

 arch/sh/mm/consistent.c                   |    6 ++++--

 arch/sparc/include/asm/dma-mapping.h      |   18 ++++++++++++------

 arch/sparc/kernel/iommu.c                 |   10 ++++++----

 arch/sparc/kernel/ioport.c                |   18 ++++++++++--------

 arch/sparc/kernel/pci_sun4v.c             |    9 +++++----

 arch/unicore32/include/asm/dma-mapping.h  |   18 ++++++++++++------

 arch/unicore32/mm/dma-swiotlb.c           |    4 ++--

 arch/x86/include/asm/dma-mapping.h        |   26 ++++++++++++++++----------

 arch/x86/kernel/amd_gart_64.c             |   11 ++++++-----

 arch/x86/kernel/pci-calgary_64.c          |    9 +++++----

 arch/x86/kernel/pci-dma.c                 |    3 ++-

 arch/x86/kernel/pci-nommu.c               |    6 +++---

 arch/x86/kernel/pci-swiotlb.c             |   12 +++++++-----

 arch/x86/xen/pci-swiotlb-xen.c            |    4 ++--

 drivers/iommu/amd_iommu.c                 |   10 ++++++----

 drivers/iommu/intel-iommu.c               |    9 +++++----

 drivers/xen/swiotlb-xen.c                 |    5 +++--

 include/linux/dma-attrs.h                 |    2 ++

 include/linux/dma-mapping.h               |   13 +++++++++----

 include/linux/swiotlb.h                   |    6 ++++--

 include/xen/swiotlb-xen.h                 |    6 ++++--

 lib/swiotlb.c                             |    5 +++--

 43 files changed, 305 insertions(+), 182 deletions(-)