linux-kernel - [PATCH v7 1/5] doc: dma-buf: List the heaps by name

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Message-Id: <20250721-dma-buf-ecc-heap-v7-1-031836e1a942@kernel.org>
Date: Mon, 21 Jul 2025 13:17:30 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>, 
 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>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Marek Szyprowski <m.szyprowski@...sung.com>, 
 Robin Murphy <robin.murphy@....com>, Jonathan Corbet <corbet@....net>
Cc: Andrew Davis <afd@...com>, Jared Kangas <jkangas@...hat.com>, 
 Mattijs Korpershoek <mkorpershoek@...nel.org>, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
 dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
 iommu@...ts.linux.dev, linux-doc@...r.kernel.org, 
 Maxime Ripard <mripard@...nel.org>
Subject: [PATCH v7 1/5] doc: dma-buf: List the heaps by name

Since we're going to introduce multiple instances of the CMA heap
driver, there's no single CMA heap anymore.

Let's use the heap name instead to differentiate between all the heaps
available in the system.

While we're at it, let's also rework the backward compatibility part to
make it easier to amend later on.

Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 Documentation/userspace-api/dma-buf-heaps.rst | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
index 1dfe5e7acd5a3c674323775176d81944147e40c0..17bf6829efd7963bc849765db54d327644e8c395 100644
--- a/Documentation/userspace-api/dma-buf-heaps.rst
+++ b/Documentation/userspace-api/dma-buf-heaps.rst
@@ -14,15 +14,16 @@ Heaps
 A heap represents a specific allocator. The Linux kernel currently supports the
 following heaps:

  - The ``system`` heap allocates virtually contiguous, cacheable, buffers.

- - The ``cma`` heap allocates physically contiguous, cacheable,
-   buffers. Only present if a CMA region is present. Such a region is
-   usually created either through the kernel commandline through the
-   ``cma`` parameter, a memory region Device-Tree node with the
-   ``linux,cma-default`` property set, or through the ``CMA_SIZE_MBYTES`` or
-   ``CMA_SIZE_PERCENTAGE`` Kconfig options. The heap's name in devtmpfs is
-   ``default_cma_region``. For backwards compatibility, when the
-   ``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option is set, a duplicate node is
-   created following legacy naming conventions; the legacy name might be
-   ``reserved``, ``linux,cma``, or ``default-pool``.
+ - The ``default_cma_region`` heap allocates physically contiguous,
+   cacheable, buffers. Only present if a CMA region is present. Such a
+   region is usually created either through the kernel commandline
+   through the ``cma`` parameter, a memory region Device-Tree node with
+   the ``linux,cma-default`` property set, or through the
+   ``CMA_SIZE_MBYTES`` or ``CMA_SIZE_PERCENTAGE`` Kconfig options. Prior
+   to Linux 6.17, its name wasn't stable and could be called
+   ``reserved``, ``linux,cma``, or ``default-pool``, depending on the
+   platform. From Linux 6.17 onwards, the creation of these heaps is
+   controlled through the ``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option for
+   backwards compatibility.

-- 
2.50.1