Re: [RFC PATCH 1/5] dt-bindings: dma: Add CMA Heap bindings

Maxime Ripard
2025-02-12T11:03:14Z

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On Wed, Feb 12, 2025 at 10:29:32AM +0000, Florent Tomasin wrote:
>
>
> On 12/02/2025 10:01, Maxime Ripard wrote:
> > On Wed, Feb 12, 2025 at 09:49:56AM +0000, Florent Tomasin wrote:
> >> Note that the CMA patches were initially shared to help reproduce my
> >> environment of development, I can isolate them in a separate patch
> >> series and include a reference or "base-commit:" tag to it in the
> >> Panthor protected mode RFC, to help progress this review in another
> >> thread. It will avoid overlapping these two topics:
> >>
> >> - Multiple standalone CMA heaps support
> >> - Panthor protected mode handling
> >
> > You keep insisting on using CMA here, but it's really not clear to me
> > why you would need CMA in the first place.
> >
> > By CMA, do you mean the CMA allocator, and thus would provide buffers
> > through the usual dma_alloc_* API, or would any allocator providing
> > physically contiguous memory work?
>
> You are correct only the CMA allocator is relevant. I needed a way to
> sub-allocate from a carved-out memory.

I'm still confused, sorry. You're saying that you require CMA but...

> > In the latter case, would something like this work:
> > https://lore.kernel.org/all/20240515-dma-buf-ecc-heap-v1-1-54cbbd049511@kernel.org/
>
> Thanks for sharing this link, I was not aware previous work was done
> on this aspect. The new carveout heap introduced in the series could
> probably be a good alternative. I will play-around with it and share
> some updates.

... you seem to be ok with a driver that doesn't use it?

Maxime

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