linux-kernel - [PATCH] Documentation: dma-buf: heaps: Add naming guidelines

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Message-Id: <20250520-dma-buf-heap-names-doc-v1-1-ab31f74809ee@kernel.org>
Date: Tue, 20 May 2025 12:00:53 +0200
From: Maxime Ripard <mripard@...nel.org>
To: 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>, Jonathan Corbet <corbet@....net>
Cc: linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 linaro-mm-sig@...ts.linaro.org, linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Maxime Ripard <mripard@...nel.org>
Subject: [PATCH] Documentation: dma-buf: heaps: Add naming guidelines

We've discussed a number of times of how some heap names are bad, but
not really what makes a good heap name.

Let's document what we expect the heap names to look like.

Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 Documentation/userspace-api/dma-buf-heaps.rst | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
index 535f49047ce6450796bf4380c989e109355efc05..b24618e360a9a9ba0bd85135d8c1760776f1a37f 100644
--- a/Documentation/userspace-api/dma-buf-heaps.rst
+++ b/Documentation/userspace-api/dma-buf-heaps.rst
@@ -21,5 +21,24 @@ following heaps:
    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. Depending on the platform, it
    might be called ``reserved``, ``linux,cma``, or ``default-pool``.
+
+Naming Convention
+=================
+
+A good heap name is a name that:
+
+- Is stable, and won't change from one version to the other;
+
+- Describes the memory region the heap will allocate from, and will
+  uniquely identify it in a given platform;
+
+- Doesn't use implementation details, such as the allocator;
+
+- Can describe intended usage.
+
+For example, assuming a platform with a reserved memory region located
+at the RAM address 0x42000000, intended to allocate video framebuffers,
+and backed by the CMA kernel allocator. Good names would be
+`memory@...00000` or `video@...00000`, but `cma-video` wouldn't.

---
base-commit: 92a09c47464d040866cf2b4cd052bc60555185fb
change-id: 20250520-dma-buf-heap-names-doc-31261aa0cfe6

Best regards,
-- 
Maxime Ripard <mripard@...nel.org>