[PATCH v3] Documentation: dma-buf: heaps: Add naming guidelines

[Andrew Davis]

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 <bagasdotme at gmail.com>
> Signed-off-by: Maxime Ripard <mripard at 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-v2-1-8ae43174cdbf@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-ab31f74809ee@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 at 42000000-cacheable-contiguous`` or ``video at 42000000``, but

You dropped "cacheable" but left it here in the suggested names, maybe
replace with "protected" here. Otherwise, LGTM,

Reviewed-by: Andrew Davis <afd at ti.com>

> +``cma-video`` wouldn't.
> 
> ---
> base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
> change-id: 20250520-dma-buf-heap-names-doc-31261aa0cfe6
> 
> Best regards,