Re: [PATCH v3 3/4] dt-bindings: reserved-memory: Make DMA-BUF CMA heap DT-configurable

[Hridya Valsaraju <hridya@google.com>]

On Thu, Jan 14, 2021 at 6:01 AM Rob Herring <robh@kernel.org> wrote:
>
> On Tue, Jan 12, 2021 at 05:21:42PM -0800, Minchan Kim wrote:
> > From: Hyesoo Yu <hyesoo.yu@samsung.com>
> >
> > Document devicetree binding for chunk cma heap on dma heap framework.
> >
> > The DMA chunk heap supports the bulk allocation of higher order pages.
>
> Why do we need this? What does this do that CMA doesn't?
>
> With a CMA area I can believe a carve out is a common, OS independent
> thing. This looks too closely tied to some Linux thing to go into DT.

Hello Rob,

Thank you for the review!

The chunk heap's allocator also allocates from the CMA area. It is,
however, optimized to perform bulk allocation of higher order pages in
an efficient manner. For this purpose, the heap needs an exclusive CMA
area that will only be used for allocation by the heap. This is the
reason why we need to use the DT to create and configure a reserved
memory region for use by the chunk CMA heap driver. Since all
allocation from DMA-BUF heaps happen from the user-space, there is no
other appropriate device-driver that we can use to register the chunk
CMA heap and configure the reserved memory region for its use.

We have been following your guidance in [1] to bind the chunk CMA heap
driver directly to the reserved_memory region it will allocate from.
Is there an alternative that we are missing Rob?

[1]: https://lore.kernel.org/lkml/20191025225009.50305-2-john.stultz@linaro.org/T/#m3dc63acd33fea269a584f43bb799a876f0b2b45d

The use-case that we have for the heap currently will allocate memory
from it from userspace and use the allocated memory to optimize
4K/8K HDR video playback with a secure DRM HW pipeline.

Thank you for all the help and review :)

Regards,
Hridya






>
> >
> > Signed-off-by: Hyesoo Yu <hyesoo.yu@samsung.com>
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > Signed-off-by: Hridya Valsaraju <hridya@google.com>
> > Change-Id: I8fb231e5a8360e2d8f65947e155b12aa664dde01
>
> Drop this.
>
> > ---
> >  .../reserved-memory/dma_heap_chunk.yaml       | 58 +++++++++++++++++++
> >  1 file changed, 58 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..3e7fed5fb006
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/reserved-memory/dma_heap_chunk.yaml
> > @@ -0,0 +1,58 @@
> > +# 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@samsung.com>
> > +  - John Stultz <john.stultz@linaro.org>
> > +  - Minchan Kim <minchan@kernel.org>
> > +  - Hridya Valsaraju<hridya@google.com>
>
> space                  ^
>
> > +
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - dma_heap,chunk
>
> The format is <vendor>,<something> and 'dma_heap' is not a vendor.
>
> > +
> > +  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>;
> > +            alignment = <0x0 0x00010000>;
> > +            chunk-order = <4>;
> > +        };
> > +    };
> > +
> > +
> > --
> > 2.30.0.284.gd98b1dd5eaa7-goog
> >