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Subject[RFC v2 0/2] Introduce DMA buffer sharing mechanism
Hello Everyone,

This is RFC v2 for DMA buffer sharing mechanism - changes from v1 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 <>, Rob Clark <> and
Daniel Vetter <>.

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


Patchset based on top of 3.2-rc3, the current version can be found at
Branch: dma-buf-upstr-v2

Earlier version at:

Best regards,
~Sumit Semwal


- Review comments incorporated:
- from Tomasz Stanislawski []
- kzalloc moved out of critical section
- corrected some in-code comments

- from Dave Airlie []

- from Daniel Vetter and Rob Clark []
- 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

v1: original

Sumit Semwal (2):
dma-buf: Introduce dma buffer sharing mechanism
dma-buf: Documentation for buffer sharing framework

Documentation/dma-buf-sharing.txt | 223 ++++++++++++++++++++++++++++
drivers/base/Kconfig | 10 ++
drivers/base/Makefile | 1 +
drivers/base/dma-buf.c | 290 +++++++++++++++++++++++++++++++++++++
include/linux/dma-buf.h | 176 ++++++++++++++++++++++
5 files changed, 700 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


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