1 files changed, 49 insertions, 10 deletions
diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
index 1dfe5e7acd5a..05445c83b79a 100644
--- a/Documentation/userspace-api/dma-buf-heaps.rst
+++ b/Documentation/userspace-api/dma-buf-heaps.rst
@@ -16,13 +16,52 @@ 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.
+
+ - A heap will be created for each reusable region in the device tree
+   with the ``shared-dma-pool`` compatible, using the full device tree
+   node name as its name. The buffer semantics are identical to
+   ``default-cma-region``.
+
+Naming Convention
+=================
+
+``dma-buf`` heaps name should meet a number of constraints:
+
+- The name must be stable, and must not change from one version to the other.
+  Userspace identifies heaps by their name, so if the names ever change, we
+  would be likely to introduce regressions.
+
+- The name must describe the memory region the heap will allocate from, and
+  must uniquely identify it in a given platform. Since userspace applications
+  use the heap name as the discriminant, it must be able to tell which heap it
+  wants to use reliably if there's multiple heaps.
+
+- The name must not mention implementation details, such as the allocator. The
+  heap driver will change over time, and implementation details when it was
+  introduced might not be relevant in the future.
+
+- The name should describe properties of the buffers that would be allocated.
+  Doing so will make heap identification easier for userspace. Such properties
+  are:
+
+  - ``contiguous`` for physically contiguous buffers;
+
+  - ``protected`` for encrypted buffers not accessible the OS;
+
+- The name may describe intended usage. Doing so will make heap identification
+  easier for userspace applications and users.
+
+For example, assuming a platform with a reserved memory region located
+at the RAM address 0x42000000, intended to allocate video framebuffers,
+physically contiguous, and backed by the CMA kernel allocator, good
+names would be ``memory@42000000-contiguous`` or ``video@42000000``, but
+``cma-video`` wouldn't.