98 lines
3.2 KiB
YAML
98 lines
3.2 KiB
YAML
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# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
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%YAML 1.2
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---
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$id: http://devicetree.org/schemas/reserved-memory/shared-dma-pool.yaml#
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$schema: http://devicetree.org/meta-schemas/core.yaml#
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title: /reserved-memory DMA pool
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maintainers:
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- devicetree-spec@vger.kernel.org
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allOf:
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- $ref: "reserved-memory.yaml"
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properties:
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compatible:
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oneOf:
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- const: shared-dma-pool
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description: >
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This indicates a region of memory meant to be used as a shared
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pool of DMA buffers for a set of devices. It can be used by an
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operating system to instantiate the necessary pool management
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subsystem if necessary.
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- const: restricted-dma-pool
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description: >
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This indicates a region of memory meant to be used as a pool
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of restricted DMA buffers for a set of devices. The memory
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region would be the only region accessible to those devices.
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When using this, the no-map and reusable properties must not
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be set, so the operating system can create a virtual mapping
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that will be used for synchronization. The main purpose for
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restricted DMA is to mitigate the lack of DMA access control
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on systems without an IOMMU, which could result in the DMA
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accessing the system memory at unexpected times and/or
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unexpected addresses, possibly leading to data leakage or
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corruption. The feature on its own provides a basic level of
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protection against the DMA overwriting buffer contents at
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unexpected times. However, to protect against general data
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leakage and system memory corruption, the system needs to
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provide way to lock down the memory access, e.g., MPU. Note
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that since coherent allocation needs remapping, one must set
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up another device coherent pool by shared-dma-pool and use
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dma_alloc_from_dev_coherent instead for atomic coherent
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allocation.
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linux,cma-default:
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type: boolean
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description: >
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If this property is present, then Linux will use the region for
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the default pool of the contiguous memory allocator.
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linux,dma-default:
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type: boolean
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description: >
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If this property is present, then Linux will use the region for
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the default pool of the consistent DMA allocator.
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if:
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properties:
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compatible:
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contains:
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const: restricted-dma-pool
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then:
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properties:
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no-map: false
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reusable: false
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unevaluatedProperties: false
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examples:
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- |
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reserved-memory {
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#address-cells = <1>;
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#size-cells = <1>;
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ranges;
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/* global autoconfigured region for contiguous allocations */
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linux,cma {
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compatible = "shared-dma-pool";
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reusable;
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size = <0x4000000>;
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alignment = <0x2000>;
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linux,cma-default;
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};
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display_reserved: framebuffer@78000000 {
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reg = <0x78000000 0x800000>;
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};
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restricted_dma_reserved: restricted-dma-pool@50000000 {
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compatible = "restricted-dma-pool";
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reg = <0x50000000 0x4000000>;
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};
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};
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...
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