Commit b12fe999 authored by Claire Chang's avatar Claire Chang Committed by Konrad Rzeszutek Wilk
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dt-bindings: of: Add restricted DMA pool 



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: default avatarClaire Chang <tientzu@chromium.org>
Tested-by: default avatarStefano Stabellini <sstabellini@kernel.org>
Tested-by: default avatarWill Deacon <will@kernel.org>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 0b84e4f8

Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt

+33 −3
Original line number Diff line number Diff line
@@ -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>;

		/* ... */

	};

};