Hello Jared,

On Mon, 7 Jul 2025 at 18:40, Jared Kangas jkangas@redhat.com wrote:

On Tue, Jun 10, 2025 at 06:12:28AM -0700, Jared Kangas wrote:

...

Hi all,

This patch series is based on a previous discussion around CMA heap naming. [1] The heap's name depends on the device name, which is generally "reserved", "linux,cma", or "default-pool", but could be any arbitrary name given to the default CMA area in the devicetree. For a consistent userspace interface, the series introduces a constant name for the CMA heap, and for backwards compatibility, an additional Kconfig that controls the creation of a legacy-named heap with the same CMA backing.

The ideas to handle backwards compatibility in [1] are to either use a symlink or add a heap node with a duplicate minor. However, I assume that we don't want to create symlinks in /dev from module initcalls, and attempting to duplicate minors would cause device_create() to fail. Because of these drawbacks, after brainstorming with Maxime Ripard, I went with creating a new node in devtmpfs with its own minor. This admittedly makes it a little unclear that the old and new nodes are backed by the same heap when both are present. The only approach that I think would provide total clarity on this in userspace is symlinking, which seemed like a fairly involved solution for devtmpfs, but if I'm wrong on this, please let me know.

Changelog:

v4:

• Fix ERR_PTR() usage for negative return value.

v3:

• Extract documentation markup fix to separate patch.
• Adjust DEFAULT_CMA_NAME per discussion in [2].
• Warn if the legacy heap name and the default heap name are the same.
• Fix DMABUF_HEAPS_CMA_LEGACY prompt.
• Touch up commit log wording.

v2:

• Use tabs instead of spaces for large vertical alignment.

Jared Kangas (3): Documentation: dma-buf: heaps: Fix code markup dma-buf: heaps: Parameterize heap name in __add_cma_heap() dma-buf: heaps: Give default CMA heap a fixed name

Documentation/userspace-api/dma-buf-heaps.rst | 11 +++--- drivers/dma-buf/heaps/Kconfig | 10 ++++++ drivers/dma-buf/heaps/cma_heap.c | 36 +++++++++++++++---- 3 files changed, 46 insertions(+), 11 deletions(-)

-- 2.49.0

Hi Sumit,

Just wanted to check in on this since discussion has died down this iteration: what's the status on this series? If there's anything I can do to help, I'm happy to lend a hand.

I'm sorry, I had to be out for a bit due to some personal reasons; overall it looks good to me. I'll apply it very soon.

Thank you for your patience!

Thanks, Jared

Best, Sumit.