Hello Everyone, Post some discussion as an RFC, here is the patch for introducing DMA buffer sharing mechanism - change history is 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, amongst others. This patch attempts 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, associated with a file pointer and allocator-defined operations for this buffer object. This operation is called the 'export' operation. - different devices to 'attach' themselves to this buffer object, to facilitate backing storage negotiation, using dma_buf_attach() API. - 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 buffer object's scatterlist using map_dma_buf and unmap_dma_buf operations. Documentation present in the patch-set gives more details. For 1st version, dma-buf is marked as an EXPERIMENTAL driver, which we can remove for later versions with additional usage and testing. *IMPORTANT*: [see https://lkml.org/lkml/2011/12/20/211 for more details] For this first version, A buffer shared using the dma_buf sharing API: - *may* be exported to user space using "mmap" *ONLY* by exporter, outside of this framework. - may be used *ONLY* by importers that do not need CPU access to the buffer. This is based on design suggestions from many people at the mini-summits, most notably from Arnd Bergmann <arnd@xxxxxxxx>, Rob Clark <rob@xxxxxx> and Daniel Vetter <daniel@xxxxxxxx>. The implementation is inspired from proof-of-concept patch-set from Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx>, who demonstrated buffer sharing between two v4l2 devices. [2] Some sample implementations and WIP for dma-buf users and exporters are available at [3] and [4]. [These are not being submitted for discussion / inclusion right now, but are for reference only] References: [1]: https://wiki.linaro.org/OfficeofCTO/MemoryManagement [2]: http://lwn.net/Articles/454389 [3]: Dave Airlie's prime support: http://cgit.freedesktop.org/~airlied/linux/log/?h=drm-prime-dmabuf [4]: Rob Clark's sharing between DRM and V4L2: https://github.com/robclark/kernel-omap4/commits/drmplane-dmabuf Patchset based on top of 3.2-rc7, the current version can be found at http://git.linaro.org/gitweb?p=people/sumitsemwal/linux-3.x.git Branch: dmabuf-patch-v1 Earlier versions: RFC: v3 at: https://lkml.org/lkml/2011/12/19/50 v2 at: https://lkml.org/lkml/2011/12/2/53 v1 at: https://lkml.org/lkml/2011/10/11/92 Wish you all happy vacations and a very happy, joyous and prosperous new year 2012 :) Best regards, ~Sumit Semwal History: v4: - Review comments incorporated: - from Konrad Rzeszutek Wilk [https://lkml.org/lkml/2011/12/20/209] - corrected language in some comments - re-ordered struct definitions for readability - added might_sleep() call in dma_buf_map_attachment() wrapper - from Rob Clark [https://lkml.org/lkml/2011/12/23/196] - Made dma-buf EXPERIMENTAL for 1st version. 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 (3): dma-buf: Introduce dma buffer sharing mechanism dma-buf: Documentation for buffer sharing framework dma-buf: mark EXPERIMENTAL for 1st release. Documentation/dma-buf-sharing.txt | 224 ++++++++++++++++++++++++++++ drivers/base/Kconfig | 11 ++ drivers/base/Makefile | 1 + drivers/base/dma-buf.c | 291 +++++++++++++++++++++++++++++++++++++ include/linux/dma-buf.h | 176 ++++++++++++++++++++++ 5 files changed, 703 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 -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
