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    SubjectRe: Linux 3.4-rc1
    On Tuesday 03 April 2012, Kyungmin Park wrote:
    > >
    > > - DMA-mapping framework. The tree now has a few more acks from
    > > people, and it's largely in the same situation as HSI is: I'll
    > > probably pull, but I really wanted the users who are impacted to
    > > actually talk to me about it.
    > >
    > Hi,
    > Now Marek and Nvidia persons are used it for DMA mapping based IOMMU.
    > Are there other person who help to merge it?
    > (+CC related persons).

    I can give a little more background information.

    We used to have separate implementations of dma_map_ops for each
    architecture that had the need to abstract dma_alloc_coherent
    and dma_map_* across both IOMMU and linear (virt_to_bus style)
    mappings and/or swiotlb. Those dma_map_ops imlpementations were
    already merged before the start of the git history and subsequently
    got used on powerpc, ia64, x86_64, sparc, alpha, mips, unicore32
    and hexagon, roughly in that order.

    We are seeing lots of IOMMUs come up on ARM now, but unfortunately
    the existing dma_map_ops do not cover the need on ARM to have
    two different kind of coherent memory (write-combine and not
    write-combine) that we have traditionally abstracted using
    the dma_alloc_coherent and dma_alloc_writecombine functions on both
    arm and avr32. In order to support IOMMUs on ARM using the same
    API as everyone else, I've asked Marek to use dma_map_ops on
    ARM, which requires slightly extending the include/linux/dma-mapping.h
    interfaces so they cover this variation.

    The actually interesting work to implement a better abstraction for
    IOMMUs, building the dma-mapping.h API on top of the iommu.h API
    in an architecture independent way has also been implemented but
    requires these changes as a prerequisite.


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