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    Subject[PATCH 0/3] Introduce DMA buffer sharing mechanism
    Date
    Hello Everyone,

    Post some discussion as an RFC, here is the patch for introducing
    DMA buffer sharing mechanism - change history is in the changelog below.

    Various subsystems - V4L2, GPU-accessors, DRI to name a few - have felt the
    need to have a common mechanism to share memory buffers across different
    devices - ARM, video hardware, GPU.

    This need comes forth from a variety of use cases including cameras, image
    processing, video recorders, sound processing, DMA engines, GPU and display
    buffers, amongst others.

    This patch attempts to define such a buffer sharing mechanism - it is the
    result of discussions from a couple of memory-management mini-summits held by
    Linaro to understand and address common needs around memory management. [1]

    A new dma_buf buffer object is added, with operations and API to allow easy
    sharing of this buffer object across devices.

    The framework allows:
    - a new buffer object to be created with fixed size, associated with a file
    pointer and allocator-defined operations for this buffer object. This
    operation is called the 'export' operation.
    - different devices to 'attach' themselves to this buffer object, to facilitate
    backing storage negotiation, using dma_buf_attach() API.
    - this exported buffer object to be shared with the other entity by asking for
    its 'file-descriptor (fd)', and sharing the fd across.
    - a received fd to get the buffer object back, where it can be accessed using
    the associated exporter-defined operations.
    - the exporter and user to share the buffer object's scatterlist using
    map_dma_buf and unmap_dma_buf operations.

    Documentation present in the patch-set gives more details.

    For 1st version, dma-buf is marked as an EXPERIMENTAL driver, which we can
    remove for later versions with additional usage and testing.

    *IMPORTANT*: [see https://lkml.org/lkml/2011/12/20/211 for more details]
    For this first version, A buffer shared using the dma_buf sharing API:
    - *may* be exported to user space using "mmap" *ONLY* by exporter, outside of
    this framework.
    - may be used *ONLY* by importers that do not need CPU access to the buffer.

    This is based on design suggestions from many people at the mini-summits,
    most notably from Arnd Bergmann <arnd@arndb.de>, Rob Clark <rob@ti.com> and
    Daniel Vetter <daniel@ffwll.ch>.

    The implementation is inspired from proof-of-concept patch-set from
    Tomasz Stanislawski <t.stanislaws@samsung.com>, who demonstrated buffer sharing
    between two v4l2 devices. [2]

    Some sample implementations and WIP for dma-buf users and exporters are
    available at [3] and [4]. [These are not being submitted for discussion /
    inclusion right now, but are for reference only]

    References:
    [1]: https://wiki.linaro.org/OfficeofCTO/MemoryManagement
    [2]: http://lwn.net/Articles/454389
    [3]: Dave Airlie's prime support:
    http://cgit.freedesktop.org/~airlied/linux/log/?h=drm-prime-dmabuf
    [4]: Rob Clark's sharing between DRM and V4L2:
    https://github.com/robclark/kernel-omap4/commits/drmplane-dmabuf

    Patchset based on top of 3.2-rc7, the current version can be found at

    http://git.linaro.org/gitweb?p=people/sumitsemwal/linux-3.x.git
    Branch: dmabuf-patch-v1

    Earlier versions:
    RFC:
    v3 at: https://lkml.org/lkml/2011/12/19/50
    v2 at: https://lkml.org/lkml/2011/12/2/53
    v1 at: https://lkml.org/lkml/2011/10/11/92

    Wish you all happy vacations and a very happy, joyous and prosperous new year
    2012 :)

    Best regards,
    ~Sumit Semwal

    History:
    v4:
    - Review comments incorporated:
    - from Konrad Rzeszutek Wilk [https://lkml.org/lkml/2011/12/20/209]
    - corrected language in some comments
    - re-ordered struct definitions for readability
    - added might_sleep() call in dma_buf_map_attachment() wrapper

    - from Rob Clark [https://lkml.org/lkml/2011/12/23/196]
    - Made dma-buf EXPERIMENTAL for 1st version.

    v3:
    - Review comments incorporated:
    - from Konrad Rzeszutek Wilk [https://lkml.org/lkml/2011/12/3/45]
    - replaced BUG_ON with WARN_ON - various places
    - added some error-checks
    - replaced EXPORT_SYMBOL with EXPORT_SYMBOL_GPL
    - some cosmetic / documentation comments

    - from Arnd Bergmann, Daniel Vetter, Rob Clark
    [https://lkml.org/lkml/2011/12/5/321]
    - removed mmap() fop and dma_buf_op, also the sg_sync* operations, and
    documented that mmap is not allowed for exported buffer
    - updated documentation to clearly state when migration is allowed
    - changed kconfig
    - some error code checks

    - from Rob Clark [https://lkml.org/lkml/2011/12/5/572]
    - update documentation to allow map_dma_buf to return -EINTR

    v2:
    - Review comments incorporated:
    - from Tomasz Stanislawski [https://lkml.org/lkml/2011/10/14/136]
    - kzalloc moved out of critical section
    - corrected some in-code comments

    - from Dave Airlie [https://lkml.org/lkml/2011/11/25/123]

    - from Daniel Vetter and Rob Clark [https://lkml.org/lkml/2011/11/26/53]
    - use struct sg_table in place of struct scatterlist
    - rename {get,put}_scatterlist to {map,unmap}_dma_buf
    - add new wrapper APIs dma_buf_{map,unmap}_attachment for ease of users

    - documentation updates as per review comments from Randy Dunlap
    [https://lkml.org/lkml/2011/10/12/439]

    v1: original


    Sumit Semwal (3):
    dma-buf: Introduce dma buffer sharing mechanism
    dma-buf: Documentation for buffer sharing framework
    dma-buf: mark EXPERIMENTAL for 1st release.

    Documentation/dma-buf-sharing.txt | 224 ++++++++++++++++++++++++++++
    drivers/base/Kconfig | 11 ++
    drivers/base/Makefile | 1 +
    drivers/base/dma-buf.c | 291 +++++++++++++++++++++++++++++++++++++
    include/linux/dma-buf.h | 176 ++++++++++++++++++++++
    5 files changed, 703 insertions(+), 0 deletions(-)
    create mode 100644 Documentation/dma-buf-sharing.txt
    create mode 100644 drivers/base/dma-buf.c
    create mode 100644 include/linux/dma-buf.h

    --
    1.7.5.4



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