Hello Everyone,
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 the first attempt in defining 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 get_scatterlist and put_scatterlist 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
Sumit Semwal (2): dma-buf: Introduce dma buffer sharing mechanism dma-buf: Documentation for buffer sharing framework
Documentation/dma-buf-sharing.txt | 210 ++++++++++++++++++++++++++++++++ drivers/base/Kconfig | 10 ++ drivers/base/Makefile | 1 + drivers/base/dma-buf.c | 242 +++++++++++++++++++++++++++++++++++++ include/linux/dma-buf.h | 162 +++++++++++++++++++++++++ 5 files changed, 625 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