Re: [PATCH 0/7] dma-buf: heaps: Turn heaps into modules

[John Stultz <jstultz@google.com>]

On Thu, Feb 26, 2026 at 2:18 AM Maxime Ripard <mripard@kernel.org> wrote:
> On Wed, Feb 25, 2026 at 10:51:30AM -0800, John Stultz wrote:
> > So heaps-as-modules is common in the Android kernels, and was
> > attempted to be upstreamed long ago:
> >   https://lore.kernel.org/lkml/20191025234834.28214-1-john.stultz@linaro.org/
> >
> > And it got a fairly chilly reception, but maybe having the additional
> > optee heap (as well as other proposed heaps) might sway folks on this
> > now.
>
> I didn't know that Android was using heap as modules only, but I'd say
> that it's even more of a reason to upstream it then.
>
> > There is also the kref bits you might need (which Android still carries):
> >   https://lore.kernel.org/lkml/20200725032633.125006-1-john.stultz@linaro.org/
>
> I'm curious about this one though. It looks like you add refcounting,
> but never really get the references anywhere. What was your intent, that
> on every allocation the buffer would get a reference to the heap so we
> avoid removing a heap with allocated buffers?

Oh, apologies I mixed this up. You can ignore that suggestion.

In Android, once folks were familiar with thinking about dma-buf
heaps, some (out of tree) drivers wanted to be able to internally
allocate from a given heap (somewhat of a hold-over from the old ION
drivers). So we have a convenience patch to provide that:
   https://android.googlesource.com/kernel/common/+/8e1ec97355ef9927e82ec18c98312bdcd80bf289%5E%21/

And since we return a dma_heap to the driver to allocate against:
  https://android.googlesource.com/kernel/common/+/fc1310ebf8fe25ea7b983400e6fa41f5a6d11966%5E%21/

The kref bit is to make sure we're doing proper reference counting on
that shared pointer.

This ended up getting bundled together along with the heaps-as-modules
changes in our out-of-tree changes, and I just confused its use here.

thanks
-john