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