Re: [Linaro-mm-sig] [PATCH 4/4] dma-heap: Devicetree binding for chunk heap

On Tue, Nov 17, 2020 at 07:00:54PM -0800, John Stultz wrote:

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 +--- +$id: https://protect2.fireeye.com/v1/url?k=9020a1f6-cfbb98fd-90212ab9-002590f5b90... +$schema: https://protect2.fireeye.com/v1/url?k=876fa02f-d8f49924-876e2b60-002590f5b90...

+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.kunihi...

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

Thanks for your review.

The chunk heap is not considered for device-specific reserved memory and specific driver. It is similar to system heap, but it only collects high-order pages by using specific cma-area for performance.

It is strange that there is in-tree user who registers chunk heap. (Wouldn't it be strange for some users to register the system heap?)

Is there a reason to use dma-heap framework to add cma-area for specific device ?

Even if some in-tree users register dma-heap with cma-area, the buffers could be allocated in user-land and these could be shared among other devices. For exclusive access, I guess, the device don't need to register dma-heap for cma area.

Please let me know if I misunderstood what you said.

Thanks, Regards.