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    SubjectRe: [Linaro-mm-sig] [RFC 1/2] dma-buf: Introduce dma buffer sharing mechanism
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    On Tue, Oct 11, 2011 at 10:23 AM, Sumit Semwal <sumit.semwal@ti.com> wrote:
    > This is the first step in defining a dma buffer sharing mechanism.
    >
    > A new buffer object dma_buf 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.
    > - different devices to 'attach' themselves to this buffer, to facilitate
    >  backing storage negotiation, using dma_buf_attach() API.
    > - association of a file pointer with each user-buffer and associated
    >   allocator-defined operations on that buffer. This operation is called the
    >   'export' operation.
    > - 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 scatterlist using get_scatterlist and
    >   put_scatterlist operations.
    >
    > Atleast one 'attach()' call is required to be made prior to calling the
    > get_scatterlist() operation.
    >
    > Couple of building blocks in get_scatterlist() are added to ease introduction
    > of sync'ing across exporter and users, and late allocation by the exporter.
    >
    > mmap() file operation is provided for the associated 'fd', as wrapper over the
    > optional allocator defined mmap(), to be used by devices that might need one.

    Why is this needed? it really doesn't make sense to be mmaping objects
    independent of some front-end like drm or v4l.

    how will you know what contents are in them, how will you synchronise
    access. Unless someone has a hard use-case for this I'd say we drop it
    until someone does.

    Dave.
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