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

[Maxime Ripard]

Hi John,

On Thu, Feb 26, 2026 at 10:03:21AM -0800, John Stultz wrote:
> On Thu, Feb 26, 2026 at 2:18 AM Maxime Ripard <mripard@xxxxxxxxxx> 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@xxxxxxxxxx/
> > >
> > > 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@xxxxxxxxxx/
> >
> > 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.

Understood, thanks :)

It looks like there's some people interested in doing what you described
though, so we might need your patch still.

Maxime

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