1*** Reserved memory regions *** 2 3Reserved memory is specified as a node under the /reserved-memory node. 4The operating system shall exclude reserved memory from normal usage 5one can create child nodes describing particular reserved (excluded from 6normal use) memory regions. Such memory regions are usually designed for 7the special usage by various device drivers. 8 9Parameters for each memory region can be encoded into the device tree 10with the following nodes: 11 12/reserved-memory node 13--------------------- 14#address-cells, #size-cells (required) - standard definition 15 - Should use the same values as the root node 16ranges (required) - standard definition 17 - Should be empty 18 19/reserved-memory/ child nodes 20----------------------------- 21Each child of the reserved-memory node specifies one or more regions of 22reserved memory. Each child node may either use a 'reg' property to 23specify a specific range of reserved memory, or a 'size' property with 24optional constraints to request a dynamically allocated block of memory. 25 26Following the generic-names recommended practice, node names should 27reflect the purpose of the node (ie. "framebuffer" or "dma-pool"). Unit 28address (@<address>) should be appended to the name if the node is a 29static allocation. 30 31Properties: 32Requires either a) or b) below. 33a) static allocation 34 reg (required) - standard definition 35b) dynamic allocation 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 42 acceptable to allocate from. 43 44If both reg and size are present, then the reg property takes precedence 45and size is ignored. 46 47Additional properties: 48compatible (optional) - standard definition 49 - may contain the following strings: 50 - shared-dma-pool: This indicates a region of memory meant to be 51 used as a shared pool of DMA buffers for a set of devices. It can 52 be used by an operating system to instantiate the necessary pool 53 management subsystem if necessary. 54 - vendor specific string in the form <vendor>,[<device>-]<usage> 55no-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, 58 nor permit speculative access to it under any circumstances other 59 than under the control of the device driver using the region. 60reusable (optional) - empty property 61 - The operating system can use the memory in this region with the 62 limitation that the device driver(s) owning the region need to be 63 able to reclaim it back. Typically that means that the operating 64 system can use that region to store volatile or cached data that 65 can be otherwise regenerated or migrated elsewhere. 66 67Linux implementation note: 68- If a "linux,cma-default" property is present, then Linux will use the 69 region for the default pool of the contiguous memory allocator. 70 71- If a "linux,dma-default" property is present, then Linux will use the 72 region for the default pool of the consistent DMA allocator. 73 74Device node references to reserved memory 75----------------------------------------- 76Regions in the /reserved-memory node may be referenced by other device 77nodes by adding a memory-region property to the device node. 78 79memory-region (optional) - phandle, specifier pairs to children of /reserved-memory 80 81Example 82------- 83This example defines 3 contiguous regions are defined for Linux kernel: 84one default of all device drivers (named linux,cma@72000000 and 64MiB in size), 85one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB), and 86one for multimedia processing (named multimedia-memory@77000000, 64MiB). 87 88/ { 89 #address-cells = <1>; 90 #size-cells = <1>; 91 92 memory { 93 reg = <0x40000000 0x40000000>; 94 }; 95 96 reserved-memory { 97 #address-cells = <1>; 98 #size-cells = <1>; 99 ranges; 100 101 /* global autoconfigured region for contiguous allocations */ 102 linux,cma { 103 compatible = "shared-dma-pool"; 104 reusable; 105 size = <0x4000000>; 106 alignment = <0x2000>; 107 linux,cma-default; 108 }; 109 110 display_reserved: framebuffer@78000000 { 111 reg = <0x78000000 0x800000>; 112 }; 113 114 multimedia_reserved: multimedia@77000000 { 115 compatible = "acme,multimedia-memory"; 116 reg = <0x77000000 0x4000000>; 117 }; 118 }; 119 120 /* ... */ 121 122 fb0: video@12300000 { 123 memory-region = <&display_reserved>; 124 /* ... */ 125 }; 126 127 scaler: scaler@12500000 { 128 memory-region = <&multimedia_reserved>; 129 /* ... */ 130 }; 131 132 codec: codec@12600000 { 133 memory-region = <&multimedia_reserved>; 134 /* ... */ 135 }; 136}; 137