bindings/reserved-memory/reserved-memory.txt

1 *** Reserved memory regions ***
3 Reserved memory is specified as a node under the /reserved-memory node.
4 The operating system shall exclude reserved memory from normal usage
5 one can create child nodes describing particular reserved (excluded from
6 normal use) memory regions. Such memory regions are usually designed for
9 Parameters for each memory region can be encoded into the device tree
12 /reserved-memory node
13 ---------------------
14 #address-cells, #size-cells (required) - standard definition
15     - Should use the same values as the root node
16 ranges (required) - standard definition
17     - Should be empty
19 /reserved-memory/ child nodes
20 -----------------------------
21 Each child of the reserved-memory node specifies one or more regions of
22 reserved memory. Each child node may either use a 'reg' property to
23 specify a specific range of reserved memory, or a 'size' property with
24 optional constraints to request a dynamically allocated block of memory.
26 Following the generic-names recommended practice, node names should
27 reflect the purpose of the node (ie. "framebuffer" or "dma-pool"). Unit
34    reg (required) - standard definition
36    size (required) - length based on parent's #size-cells
37                    - Size in bytes of memory to reserve.
38    alignment (optional) - length based on parent's #size-cells
39                         - Address boundary for alignment of allocation.
40    alloc-ranges (optional) - prop-encoded-array (address, length pairs).
41                            - Specifies regions of memory that are
48 compatible (optional) - standard definition
49     - may contain the following strings:
50         - shared-dma-pool: This indicates a region of memory meant to be
54         - vendor specific string in the form <vendor>,[<device>-]<usage>
55 no-map (optional) - empty property
56     - Indicates the operating system must not create a virtual mapping
57       of the region as part of its standard mapping of system memory,
60 reusable (optional) - empty property
61     - The operating system can use the memory in this region with the
67 A node must not carry both the no-map and the reusable property as these are
71 - If a "linux,cma-default" property is present, then Linux will use the
72   region for the default pool of the contiguous memory allocator.
74 - If a "linux,dma-default" property is present, then Linux will use the
77 Device node references to reserved memory
78 -----------------------------------------
79 Regions in the /reserved-memory node may be referenced by other device
80 nodes by adding a memory-region property to the device node.
82 memory-region (optional) - phandle, specifier pairs to children of /reserved-memory
83 memory-region-names (optional) - a list of names, one for each corresponding
84   entry in the memory-region property
87 -------
91 one for multimedia processing (named multimedia-memory@77000000, 64MiB).
94 	#address-cells = <1>;
95 	#size-cells = <1>;
97 	memory {
101 	reserved-memory {
102 		#address-cells = <1>;
103 		#size-cells = <1>;
108 			compatible = "shared-dma-pool";
112 			linux,cma-default;
120 			compatible = "acme,multimedia-memory";
128 		memory-region = <&display_reserved>;
133 		memory-region = <&multimedia_reserved>;
138 		memory-region = <&multimedia_reserved>;