Hello Everyone,
This is RFC v3 for DMA buffer sharing mechanism - changes from v2 are 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, and others.
This RFC is an attempt 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. - 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 map_dma_buf and unmap_dma_buf operations.
Documentation present in the patch-set gives more details.
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]
References: [1]: https://wiki.linaro.org/OfficeofCTO/MemoryManagement [2]: http://lwn.net/Articles/454389
Patchset based on top of 3.2-rc3, the current version can be found at
http://git.linaro.org/gitweb?p=people/sumitsemwal/linux-3.x.git Branch: dma-buf-upstr-v2
Earlier versions: v2 at: https://lkml.org/lkml/2011/12/2/53 v1 at: https://lkml.org/lkml/2011/10/11/92
Best regards, ~Sumit Semwal
History:
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 (2): dma-buf: Introduce dma buffer sharing mechanism dma-buf: Documentation for buffer sharing framework
Documentation/dma-buf-sharing.txt | 222 ++++++++++++++++++++++++++++ drivers/base/Kconfig | 10 ++ drivers/base/Makefile | 1 + drivers/base/dma-buf.c | 289 +++++++++++++++++++++++++++++++++++++ include/linux/dma-buf.h | 172 ++++++++++++++++++++++ 5 files changed, 694 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