doc/devicetree: Persistent memory region bindings

Add device-tree binding documentation for the nvdimm region driver.

Cc: [e-mail]
Signed-off-by: Oliver O'Halloran <[e-mail]>
Acked-by: Michael Ellerman <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>

Documentation/devicetree/bindings/pmem/pmem-region.txt

···
+Device-tree bindings for persistent memory regions
+-----------------------------------------------------
+
+Persistent memory refers to a class of memory devices that are:
+
+	a) Usable as main system memory (i.e. cacheable), and
+	b) Retain their contents across power failure.
+
+Given b) it is best to think of persistent memory as a kind of memory mapped
+storage device. To ensure data integrity the operating system needs to manage
+persistent regions separately to the normal memory pool. To aid with that this
+binding provides a standardised interface for discovering where persistent
+memory regions exist inside the physical address space.
+
+Bindings for the region nodes:
+-----------------------------
+
+Required properties:
+	- compatible = "pmem-region"
+
+	- reg = <base, size>;
+		The reg property should specificy an address range that is
+		translatable to a system physical address range. This address
+		range should be mappable as normal system memory would be
+		(i.e cacheable).
+
+		If the reg property contains multiple address ranges
+		each address range will be treated as though it was specified
+		in a separate device node. Having multiple address ranges in a
+		node implies no special relationship between the two ranges.
+
+Optional properties:
+	- Any relevant NUMA assocativity properties for the target platform.
+
+	- volatile; This property indicates that this region is actually
+	  backed by non-persistent memory. This lets the OS know that it
+	  may skip the cache flushes required to ensure data is made
+	  persistent after a write.
+
+	  If this property is absent then the OS must assume that the region
+	  is backed by non-volatile memory.
+
+Examples:
+--------------------
+
+	/*
+	 * This node specifies one 4KB region spanning from
+	 * 0x5000 to 0x5fff that is backed by non-volatile memory.
+	 */
+	pmem@5000 {
+		compatible = "pmem-region";
+		reg = <0x00005000 0x00001000>;
+	};
+
+	/*
+	 * This node specifies two 4KB regions that are backed by
+	 * volatile (normal) memory.
+	 */
+	pmem@6000 {
+		compatible = "pmem-region";
+		reg = < 0x00006000 0x00001000
+			0x00008000 0x00001000 >;
+		volatile;
+	};
+

MAINTAINERS

···
 Q:	https://patchwork.kernel.org/project/linux-nvdimm/list/
 S:	Supported
 F:	drivers/nvdimm/of_pmem.c
+F:	Documentation/devicetree/bindings/pmem/pmem-region.txt
 
 LIBNVDIMM: NON-VOLATILE MEMORY DEVICE SUBSYSTEM
 M:	Dan Williams <[e-mail]>