[Linaro-mm-sig] [RFC] dma-shared-buf: Add buffer sharing framework

[Daniel Vetter]

On Fri, Sep 02, 2011 at 10:49:44AM -0500, Clark, Rob wrote:
> oh, and if the importing driver is bracketing DMA to/from the buffer
> w/ get/put scatter list, it should even be possible to implement more
> fancy reallocation or migration stuff later if it is actually needed,
> without changing dmabuf API.  Or at least this is my theory.
> 
> The restriction is that get_sglist needs to be called only from a
> context that could block.
> 
> (And maybe needs to return some hint to the importing driver that the
> buffer location has/hasn't changed?  I'm not sure.. if we are
> returning device addresses thanks to iommu and having passed the
> 'struct device' ptr to get_sglist(), then all the optimizations of
> caching the mapping of the buffer is all behind the scenes?)

Yeah, that's the idea. It's only a small step from the 2-step api to
something with (implicit) sync objects. The easieast way would be to add a
flag to get_scatterlist to tell the core that the corresponding
put_scatterlist will happen in a short time. And another flag for
attach_device to wait for oustanding dma so that the buffer can be
re-allocated. It would obviously still return -EBUSY if there are valid
mappings with indefinit lifetime out there.
-Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
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