1Device-tree bindings for persistent memory regions 2----------------------------------------------------- 3 4Persistent memory refers to a class of memory devices that are: 5 6 a) Usable as main system memory (i.e. cacheable), and 7 b) Retain their contents across power failure. 8 9Given b) it is best to think of persistent memory as a kind of memory mapped 10storage device. To ensure data integrity the operating system needs to manage 11persistent regions separately to the normal memory pool. To aid with that this 12binding provides a standardised interface for discovering where persistent 13memory regions exist inside the physical address space. 14 15Bindings for the region nodes: 16----------------------------- 17 18Required properties: 19 - compatible = "pmem-region" 20 21 - reg = <base, size>; 22 The reg property should specificy an address range that is 23 translatable to a system physical address range. This address 24 range should be mappable as normal system memory would be 25 (i.e cacheable). 26 27 If the reg property contains multiple address ranges 28 each address range will be treated as though it was specified 29 in a separate device node. Having multiple address ranges in a 30 node implies no special relationship between the two ranges. 31 32Optional properties: 33 - Any relevant NUMA assocativity properties for the target platform. 34 35 - volatile; This property indicates that this region is actually 36 backed by non-persistent memory. This lets the OS know that it 37 may skip the cache flushes required to ensure data is made 38 persistent after a write. 39 40 If this property is absent then the OS must assume that the region 41 is backed by non-volatile memory. 42 43Examples: 44-------------------- 45 46 /* 47 * This node specifies one 4KB region spanning from 48 * 0x5000 to 0x5fff that is backed by non-volatile memory. 49 */ 50 pmem@5000 { 51 compatible = "pmem-region"; 52 reg = <0x00005000 0x00001000>; 53 }; 54 55 /* 56 * This node specifies two 4KB regions that are backed by 57 * volatile (normal) memory. 58 */ 59 pmem@6000 { 60 compatible = "pmem-region"; 61 reg = < 0x00006000 0x00001000 62 0x00008000 0x00001000 >; 63 volatile; 64 }; 65 66