linux-kernel - Re: [RFC PATCH 2/5] cma-heap: Allow registration of custom cma heaps

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Message-ID: <kyesso3gaajbdze3ie4imrmrk2lzqf6s7eoonlljeitfs3utwh@dycnl7cnzep5>
Date: Thu, 30 Jan 2025 14:34:30 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Florent Tomasin <florent.tomasin@....com>
Cc: 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 2/5] cma-heap: Allow registration of custom cma heaps

Hi,

On Thu, Jan 30, 2025 at 01:08:58PM +0000, Florent Tomasin wrote:
> This patch introduces a cma-heap probe function, allowing
> users to register custom cma heaps in the device tree.
> 
> A "memory-region" is bound to the cma heap at probe time
> allowing allocation of DMA buffers from that heap.
> 
> Use cases:
> - registration of carved out secure heaps. Some devices
>   are implementing secure memory by reserving a specific
>   memory regions for that purpose. For example, this is the
>   case of platforms making use of early version of
>   ARM TrustZone.

In such a case, the CMA heap would de-facto become un-mappable for
userspace, right?

> - registration of multiple memory regions at different
>   locations for efficiency or HW integration reasons.
>   For example, a peripheral may expect to share data at a
>   specific location in RAM. This information could have been
>   programmed by a FW prior to the kernel boot.

How would you differentiate between them?

Maxime

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