On 7/17/25 3:10 AM, Maxime Ripard wrote:
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.
Reviewed-by: Bagas Sanjaya <bagasdo...@gmail.com>
Signed-off-by: Maxime Ripard <mrip...@kernel.org>
---
Changes in v3:
- Grammar, spelling fixes
- Remove the cacheable / uncacheable name suggestion
- Link to v2:
https://lore.kernel.org/r/20250616-dma-buf-heap-names-doc-v2-1-8ae43174c...@kernel.org
Changes in v2:
- Added justifications for each requirement / suggestions
- Added a mention and example of buffer attributes
- Link to v1:
https://lore.kernel.org/r/20250520-dma-buf-heap-names-doc-v1-1-ab31f7480...@kernel.org
---
Documentation/userspace-api/dma-buf-heaps.rst | 35 +++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/Documentation/userspace-api/dma-buf-heaps.rst
b/Documentation/userspace-api/dma-buf-heaps.rst
index
535f49047ce6450796bf4380c989e109355efc05..3ee4e7961fe390ba356a2125d53b060546c3e4a6
100644
--- a/Documentation/userspace-api/dma-buf-heaps.rst
+++ b/Documentation/userspace-api/dma-buf-heaps.rst
@@ -21,5 +21,40 @@ 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
+=================
+
+``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-cacheable-contiguous`` or ``video@42000000``, but
You dropped "cacheable" but left it here in the suggested names, maybe
replace with "protected" here. Otherwise, LGTM,
Reviewed-by: Andrew Davis <a...@ti.com>
+``cma-video`` wouldn't.
---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250520-dma-buf-heap-names-doc-31261aa0cfe6
Best regards,
