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SubjectRe: [PATCH 4/4] dma-heap: Devicetree binding for chunk heap
On Tue, Nov 17, 2020 at 10:19 AM Minchan Kim <minchan@kernel.org> wrote:
>
> From: Hyesoo Yu <hyesoo.yu@samsung.com>
>
> Document devicetree binding for chunk heap on dma heap framework
>
> Signed-off-by: Hyesoo Yu <hyesoo.yu@samsung.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> .../bindings/dma-buf/chunk_heap.yaml | 52 +++++++++++++++++++
> 1 file changed, 52 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/dma-buf/chunk_heap.yaml
>
> diff --git a/Documentation/devicetree/bindings/dma-buf/chunk_heap.yaml b/Documentation/devicetree/bindings/dma-buf/chunk_heap.yaml
> new file mode 100644
> index 000000000000..f382bee02778
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma-buf/chunk_heap.yaml
> @@ -0,0 +1,52 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/dma-buf/chunk_heap.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Device tree binding for chunk heap on DMA HEAP FRAMEWORK
> +
> +maintainers:
> + - Sumit Semwal <sumit.semwal@linaro.org>
> +
> +description: |
> + The chunk heap is backed by the Contiguous Memory Allocator (CMA) and
> + allocates the buffers that are made up to a list of fixed size chunks
> + taken from CMA. Chunk sizes are configurated when the heaps are created.
> +
> +properties:
> + compatible:
> + enum:
> + - dma_heap,chunk
> +
> + memory-region:
> + maxItems: 1
> +
> + alignment:
> + maxItems: 1
> +
> +required:
> + - compatible
> + - memory-region
> + - alignment
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + reserved-memory {
> + #address-cells = <2>;
> + #size-cells = <1>;
> +
> + chunk_memory: chunk_memory {
> + compatible = "shared-dma-pool";
> + reusable;
> + size = <0x10000000>;
> + };
> + };
> +
> + chunk_default_heap: chunk_default_heap {
> + compatible = "dma_heap,chunk";
> + memory-region = <&chunk_memory>;
> + alignment = <0x10000>;
> + };


So I suspect Rob will push back on this as he has for other dt
bindings related to ion/dmabuf heaps (I tried to push a similar
solution to exporting multiple CMA areas via dmabuf heaps).

The proposal he seemed to like best was having an in-kernel function
that a driver would call to initialize the heap (associated with the
CMA region the driver is interested in). Similar to Kunihiko Hayashi's
patch here:
- https://lore.kernel.org/lkml/1594948208-4739-1-git-send-email-hayashi.kunihiko@socionext.com/

The one sticking point for that patch (which I think is a good one),
is that we don't have any in-tree users, so it couldn't be merged yet.

A similar approach might be good here, but again we probably need to
have at least one in-tree user which could call such a registration
function.

thanks
-john

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