[EARLY RFC][PATCH] dma-buf: Add dma-buf heaps framework

[John Stultz]

On Mon, Feb 25, 2019 at 6:36 AM Andrew F. Davis <afd at ti.com> wrote:
>
> This framework allows a unified userspace interface for dma-buf
> exporters, allowing userland to allocate specific types of memory
> for use in dma-buf sharing.
>
> Each heap is given its own device node, which a user can allocate
> a dma-buf fd from using the DMA_HEAP_IOC_ALLOC.
>
> Signed-off-by: Andrew F. Davis <afd at ti.com>
> ---
>
> Hello all,
>
> I had a little less time over the weekend than I thought I would to
> clean this up more and finish the first set of user heaps, but wanted
> to get this out anyway.
>
> ION in its current form assumes a lot about the memory it exports and
> these assumptions lead to restrictions on the full range of operations
> dma-buf's can produce. Due to this if we are to add this as an extension
> of the core dma-buf then it should only be the user-space advertisement
> and allocation front-end. All dma-buf exporting and operation need to be
> placed in the control of the exporting heap. The core becomes rather
> small, just a few hundred lines you see here. This is not to say we
> should not provide helpers to make the heap exporters more simple, but
> they should only be helpers and not enforced by the core framework.
>
> Basic use model here is an exporter (dedicated heap memory driver, CMA,
> System, etc.) registers with the framework by providing a struct
> dma_heap_info which gives us the needed info to export this heap to
> userspace as a device node. Next a user will request an allocation,
> the IOCTL is parsed and the request made to a heap provided alloc() op.
> The heap should return the filled out struct dma_heap_buffer, including
> exporting the buffer as a dma-buf. This dma-buf we then return to the
> user as a fd. Buffer free is still a bit open as we need to update some
> stats and free some memory, but the release operation is controlled by
> the heap exporter, so some hook will have to be created.
>
> It all needs a bit more work, and I'm sure I'll find missing parts when
> I add some more heaps, but hopefully this framework is simple enough that
> it does not impede the implementation of all functionality once provided
> by ION (shrinker, delayed free), nor any new functionality needed for
> future heap exporting devices.

Overall looks pretty good!  I'll take a stab today at reworking my
stack on top of this starting patch.

thanks
-john