On Mon, Dec 19, 2011 at 02:03:28PM +0530, Sumit Semwal wrote: > 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 <a...@arndb.de>, Rob Clark <r...@ti.com> and > Daniel Vetter <dan...@ffwll.ch>. > > The implementation is inspired from proof-of-concept patch-set from > Tomasz Stanislawski <t.stanisl...@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
I think this is a really good v1 version of dma_buf. It contains all the required bits (with well-specified semantics in the doc patch) to implement some basic use-cases and start fleshing out the integration with various subsystem (like drm and v4l). All the things still under discussion like - userspace mmap support - more advanced (and more strictly specified) coherency models - and shared infrastructure for implementing exporters are imo much clearer once we have a few example drivers at hand and a better understanding of some of the insane corner cases we need to be able to handle. And I think any risk that the resulting clarifications will break a basic use-case is really minimal, so I think it'd be great if this could go into 3.3 (maybe as some kind of staging/experimental infrastructure). Hence for both patches: Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch> -- Daniel Vetter Mail: dan...@ffwll.ch Mobile: +41 (0)79 365 57 48 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
