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Diffstat (limited to 'kernel/Documentation/devicetree/bindings/reserved-memory')
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diff --git a/kernel/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/kernel/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt new file mode 100644 index 000000000..3da0ebdba --- /dev/null +++ b/kernel/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt @@ -0,0 +1,133 @@ +*** Reserved memory regions *** + +Reserved memory is specified as a node under the /reserved-memory node. +The operating system shall exclude reserved memory from normal usage +one can create child nodes describing particular reserved (excluded from +normal use) memory regions. Such memory regions are usually designed for +the special usage by various device drivers. + +Parameters for each memory region can be encoded into the device tree +with the following nodes: + +/reserved-memory node +--------------------- +#address-cells, #size-cells (required) - standard definition + - Should use the same values as the root node +ranges (required) - standard definition + - Should be empty + +/reserved-memory/ child nodes +----------------------------- +Each child of the reserved-memory node specifies one or more regions of +reserved memory. Each child node may either use a 'reg' property to +specify a specific range of reserved memory, or a 'size' property with +optional constraints to request a dynamically allocated block of memory. + +Following the generic-names recommended practice, node names should +reflect the purpose of the node (ie. "framebuffer" or "dma-pool"). Unit +address (@<address>) should be appended to the name if the node is a +static allocation. + +Properties: +Requires either a) or b) below. +a) static allocation + reg (required) - standard definition +b) dynamic allocation + size (required) - length based on parent's #size-cells + - Size in bytes of memory to reserve. + alignment (optional) - length based on parent's #size-cells + - Address boundary for alignment of allocation. + alloc-ranges (optional) - prop-encoded-array (address, length pairs). + - Specifies regions of memory that are + acceptable to allocate from. + +If both reg and size are present, then the reg property takes precedence +and size is ignored. + +Additional properties: +compatible (optional) - standard definition + - may contain the following strings: + - shared-dma-pool: 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 instanciate the necessary pool + management subsystem if necessary. + - vendor specific string in the form <vendor>,[<device>-]<usage> +no-map (optional) - empty property + - Indicates the operating system must not create a virtual mapping + of the region as part of its standard mapping of system memory, + nor permit speculative access to it under any circumstances other + than under the control of the device driver using the region. +reusable (optional) - empty property + - The operating system can use the memory in this region with the + limitation that the device driver(s) owning the region need to be + able to reclaim it back. Typically that means that the operating + system can use that region to store volatile or cached data that + can be otherwise regenerated or migrated elsewhere. + +Linux implementation note: +- If a "linux,cma-default" property is present, then Linux will use the + region for the default pool of the contiguous memory allocator. + +Device node references to reserved memory +----------------------------------------- +Regions in the /reserved-memory node may be referenced by other device +nodes by adding a memory-region property to the device node. + +memory-region (optional) - phandle, specifier pairs to children of /reserved-memory + +Example +------- +This example defines 3 contiguous regions are defined 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). + +/ { + #address-cells = <1>; + #size-cells = <1>; + + memory { + reg = <0x40000000 0x40000000>; + }; + + 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>; + }; + + multimedia_reserved: multimedia@77000000 { + compatible = "acme,multimedia-memory"; + reg = <0x77000000 0x4000000>; + }; + }; + + /* ... */ + + fb0: video@12300000 { + memory-region = <&display_reserved>; + /* ... */ + }; + + scaler: scaler@12500000 { + memory-region = <&multimedia_reserved>; + /* ... */ + }; + + codec: codec@12600000 { + memory-region = <&multimedia_reserved>; + /* ... */ + }; +}; |