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dt-bindings: of: Add restricted DMA pool

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Introduce the new compatible string, restricted-dma-pool, for restricted
DMA. One can specify the address and length of the restricted DMA memory
region by restricted-dma-pool in the reserved-memory node.

Signed-off-by: Claire Chang <tientzu@chromium.org>
Tested-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Will Deacon <will@kernel.org>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Claire Chang 2021-06-19 11:40:42 +08:00 committed by Konrad Rzeszutek Wilk
parent 0b84e4f8b7
commit b12fe99954
1 changed files with 33 additions and 3 deletions
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36
Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
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@ -51,6 +51,23 @@ compatible (optional) - standard definition
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.
- restricted-dma-pool: 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.
- vendor specific string in the form <vendor>,[<device>-]<usage>
no-map (optional) - empty property
- Indicates the operating system must not create a virtual mapping
@ -85,10 +102,11 @@ memory-region-names (optional) - a list of names, one for each corresponding
Example
-------
This example defines 3 contiguous regions are defined for Linux kernel:
This example defines 4 contiguous regions for Linux kernel:
one default of all device drivers (named linux,cma@72000000 and 64MiB in size),
one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB), and
one for multimedia processing (named multimedia-memory@77000000, 64MiB).
one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB),
one for multimedia processing (named multimedia-memory@77000000, 64MiB), and
one for restricted dma pool (named restricted_dma_reserved@0x50000000, 64MiB).
/ {
#address-cells = <1>;
@ -120,6 +138,11 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
compatible = "acme,multimedia-memory";
reg = <0x77000000 0x4000000>;
};
restricted_dma_reserved: restricted_dma_reserved {
compatible = "restricted-dma-pool";
reg = <0x50000000 0x4000000>;
};
};
/* ... */
@ -138,4 +161,11 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
memory-region = <&multimedia_reserved>;
/* ... */
};
pcie_device: pcie_device@0,0 {
reg = <0x83010000 0x0 0x00000000 0x0 0x00100000
0x83010000 0x0 0x00100000 0x0 0x00100000>;
memory-region = <&restricted_dma_reserved>;
/* ... */
};
};