Re: [PATCH v4 3/4] dt-bindings: reserved-memory: Make DMA-BUF CMA heap DT-configurable
From: Rob Herring <robh@kernel.org>
Date: 2021-02-06 04:25:56
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On Thu, Jan 21, 2021 at 09:55:01AM -0800, Minchan Kim wrote:
From: Hyesoo Yu <redacted> Document devicetree binding for chunk cma heap on dma heap framework. The DMA chunk heap supports the bulk allocation of higher order pages. The chunk heap's allocator allocates from the CMA area. It is 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.
LWN tells me we don't need carve outs any more[1]: "CMA now relies on compaction and no longer uses a carved-out memory region." So why do we need this? [1] https://lwn.net/Articles/839216/
quoted hunk ↗ jump to hunk
Signed-off-by: Hyesoo Yu <redacted> Signed-off-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Hridya Valsaraju <redacted> --- .../reserved-memory/dma_heap_chunk.yaml | 56 +++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 Documentation/devicetree/bindings/reserved-memory/dma_heap_chunk.yamldiff --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@samsung.com> + - John Stultz <john.stultz@linaro.org> + - Minchan Kim <minchan@kernel.org> + - Hridya Valsaraju<hridya@google.com> + + +properties: + compatible: + enum: + - dma_heap,chunk
Convention is vendor,thing and 'dma_heap' is not a vendor. Also, '-' is preferred over '_'.
+ + chunk-order: + description: | + order of pages that will get allocated from the chunk DMA heap.
Page size depends on Linux configuration. And 'order' is very much a Linuxism.
+ 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>;
+ };
+ };
--
2.30.0.296.g2bfb1c46d8-goog