Re: [PATCH v4 0/3] dma-buf: heaps: Use constant name for CMA heap

[Jared Kangas <jkangas@redhat.com>]

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.
> 
> [1]: https://lore.kernel.org/all/f6412229-4606-41ad-8c05-7bbba2eb6e08@ti.com/
> [2]: https://lore.kernel.org/all/CANDhNCroe6ZBtN_o=c71kzFFaWK-fF5rCdnr9P5h1sgPOWSGSw@mail.gmail.com/
> 
> 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.

Thanks,
Jared