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

[John Stultz]

On Wed, Feb 27, 2019 at 8:38 AM Andrew F. Davis <afd at ti.com> wrote:
>
> On 2/26/19 5:40 PM, John Stultz wrote:
> > On Tue, Feb 26, 2019 at 11:21 AM John Stultz <john.stultz at linaro.org> wrote:
> > I've updated the patches here:
> > kernel: https://git.linaro.org/people/john.stultz/android-dev.git/log/?h=dev/dma-buf-heap
> > userland: https://android-review.googlesource.com/c/device/linaro/hikey/+/909436
> >
> >
> >> I also realized some of Benajmin's error path improvements are going
> >> to be hard to fix w/ my current code, specifically having the allocate
> >> op do the allocation of the dma_heap_buffer (since we don't have a
> >> free op, if something fails creating the dmabuf fd in the core, we
> >> don't have a hook to release the dma_heap_buffer and heap private
> >> data).
> >
>
> We can always add back the free op, the alternative is to have the heap
> export the fd.
>
> I'm not sure either is needed though, when we
> dma_buf_put(buffer->dmabuf) on the error path it should trigger the
> release op, and that can cleanup the allocations in the heap.

Good point, but I worry that's a bit subtle.

Also doing the stuff with the helpers where we have to register a free
callback is kind of ugly, and I personally like the symmetry of having
free hooks if we have allocation hooks (even if the dmabuf release
hook initiates the free call).

> > I also realized doing my development and testing against my
> > hikey960-mainline-WIP branch, I accidentally folded in an ion hack I
> > was using to reduce cache operations, so I'll need to undo that in the
> > heap-helpers.c.  But at least we have a rough validation point for the
> > design.
> >
>
> Great! The details of the heap-helpers can always get fixed up at a
> later point, validation of the core working is really good to hear.
>

Let me know if you have any further feedback or changes to integrate.
I've got to get back to some other work, but will try to take a
cleanup pass in the next few days.

thanks
-john