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

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Message-ID: <20250212-sweet-nano-penguin-e85e7d@houat>
Date: Wed, 12 Feb 2025 11:49:34 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Florent Tomasin <florent.tomasin@....com>
Cc: Nicolas Dufresne <nicolas@...fresne.ca>, Vinod Koul <vkoul@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Boris Brezillon <boris.brezillon@...labora.com>, 
	Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Sumit Semwal <sumit.semwal@...aro.org>, Benjamin Gaignard <benjamin.gaignard@...labora.com>, 
	Brian Starkey <Brian.Starkey@....com>, John Stultz <jstultz@...gle.com>, 
	"T . J . Mercier" <tjmercier@...gle.com>, Christian König <christian.koenig@....com>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Yong Wu <yong.wu@...iatek.com>, dmaengine@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, nd@....com, 
	Akash Goel <akash.goel@....com>
Subject: Re: [RFC PATCH 1/5] dt-bindings: dma: Add CMA Heap bindings

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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