• Sumit Semwal's avatar
    dma-buf: Introduce dma buffer sharing mechanism · d15bd7ee
    Sumit Semwal authored
    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:
    - creation of a buffer object, its association with a file pointer, and
       associated allocator-defined operations on that buffer. This operation is
       called the 'export' operation.
    - different devices to 'attach' themselves to this exported buffer object, to
      facilitate backing storage negotiation, using dma_buf_attach() API.
    - the 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 associated with this buffer
       object using map_dma_buf and unmap_dma_buf operations.
    
    Atleast one 'attach()' call is required to be made prior to calling the
    map_dma_buf() operation.
    
    Couple of building blocks in map_dma_buf() are added to ease introduction
    of sync'ing across exporter and users, and late allocation by the exporter.
    
    For this first version, this framework will work with certain conditions:
    - *ONLY* exporter will be allowed to mmap to userspace (outside of this
       framework - mmap is not a buffer object operation),
    - currently, *ONLY* users that do not need CPU access to the buffer are
       allowed.
    
    More details are there in the documentation patch.
    
    This is based on design suggestions from many people at the mini-summits[1],
    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]
    
    [1]: https://wiki.linaro.org/OfficeofCTO/MemoryManagement
    [2]: http://lwn.net/Articles/454389Signed-off-by: default avatarSumit Semwal <sumit.semwal@linaro.org>
    Signed-off-by: default avatarSumit Semwal <sumit.semwal@ti.com>
    Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    Reviewed-by: default avatarDave Airlie <airlied@redhat.com>
    Reviewed-and-Tested-by: default avatarRob Clark <rob.clark@linaro.org>
    Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
    d15bd7ee
dma-buf.c 7.44 KB