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

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Date:   Wed, 27 Jan 2021 12:25:04 -0800
From:   Hridya Valsaraju <hridya@...gle.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        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>,
        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 Mon, Jan 25, 2021 at 11:07 PM John Stultz <john.stultz@...aro.org> wrote:
>
> 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?

Thank you John, yes, that makes sense. We will add the 'reg' parameter
as well when we send out the next version.

Regards,
Hridya

>
> thanks
> -john