linux-kernel - Re: [PATCH v4 3/4] dt-bindings: reserved-memory: Make DMA-BUF CMA heap DT-configurable

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Date:   Mon, 25 Jan 2021 23:07:21 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Hyesoo Yu <hyesoo.yu@...sung.com>, david@...hat.com,
        Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        KyongHo Cho <pullip.cho@...sung.com>,
        John Dias <joaodias@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        linux-media <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Rob Herring <robh+dt@...nel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v4 3/4] dt-bindings: reserved-memory: Make DMA-BUF CMA
 heap DT-configurable

On Thu, Jan 21, 2021 at 9:55 AM Minchan Kim <minchan@...nel.org> wrote:
>  .../reserved-memory/dma_heap_chunk.yaml       | 56 +++++++++++++++++++
>  1 file changed, 56 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/reserved-memory/dma_heap_chunk.yaml
>
> diff --git a/Documentation/devicetree/bindings/reserved-memory/dma_heap_chunk.yaml b/Documentation/devicetree/bindings/reserved-memory/dma_heap_chunk.yaml
> new file mode 100644
> index 000000000000..00db0ae6af61
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/reserved-memory/dma_heap_chunk.yaml
> @@ -0,0 +1,56 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/reserved-memory/dma_heap_chunk.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Device tree binding for chunk heap on DMA HEAP FRAMEWORK
> +
> +description: |
> +  The DMA chunk heap is backed by the Contiguous Memory Allocator (CMA) and
> +  supports bulk allocation of fixed size pages.
> +
> +maintainers:
> +  - Hyesoo Yu <hyesoo.yu@...sung.com>
> +  - John Stultz <john.stultz@...aro.org>
> +  - Minchan Kim <minchan@...nel.org>
> +  - Hridya Valsaraju<hridya@...gle.com>
> +
> +
> +properties:
> +  compatible:
> +    enum:
> +      - dma_heap,chunk
> +
> +  chunk-order:
> +    description: |
> +            order of pages that will get allocated from the chunk DMA heap.
> +    maxItems: 1
> +
> +  size:
> +    maxItems: 1
> +
> +  alignment:
> +    maxItems: 1
> +
> +required:
> +  - compatible
> +  - size
> +  - alignment
> +  - chunk-order
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    reserved-memory {
> +        #address-cells = <2>;
> +        #size-cells = <1>;
> +
> +        chunk_memory: chunk_memory {
> +            compatible = "dma_heap,chunk";
> +            size = <0x3000000>;

Hey Minchan,
  Looking closer here, would it make more sense to document the "reg =
<>" parameter here as well instead of just "size = <>"?

That way the address of the region could be explicitly specified (for
instance, to ensure the CMA region created is 32bit addressable). And
more practically, trying to satisfy the base address alignment checks
in the final patch when its set dynamically may require a fair amount
of luck  - I couldn't manage it in my own testing on the hikey960 w/o
resorting to reg=  :)

It does look like the RESERVEDMEM_OF_DECLARE() logic already supports
this, so it's likely just a matter of documenting it here?

thanks
-john