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+Multi-Function Devices (MFD)
+
+These devices comprise a nexus for heterogeneous hardware blocks containing
+more than one non-unique yet varying hardware functionality.
+
+A typical MFD can be:
+
+- A mixed signal ASIC on an external bus, sometimes a PMIC (Power Management
+ Integrated Circuit) that is manufactured in a lower technology node (rough
+ silicon) that handles analog drivers for things like audio amplifiers, LED
+ drivers, level shifters, PHY (physical interfaces to things like USB or
+ ethernet), regulators etc.
+
+- A range of memory registers containing "miscellaneous system registers" also
+ known as a system controller "syscon" or any other memory range containing a
+ mix of unrelated hardware devices.
+
+Optional properties:
+
+- compatible : "simple-mfd" - this signifies that the operating system should
+ consider all subnodes of the MFD device as separate devices akin to how
+ "simple-bus" indicates when to see subnodes as children for a simple
+ memory-mapped bus. For more complex devices, when the nexus driver has to
+ probe registers to figure out what child devices exist etc, this should not
+ be used. In the latter case the child devices will be determined by the
+ operating system.
+
+- ranges: Describes the address mapping relationship to the parent. Should set
+ the child's base address to 0, the physical address within parent's address
+ space, and the length of the address map.
+
+- #address-cells: Specifies the number of cells used to represent physical base
+ addresses. Must be present if ranges is used.
+
+- #size-cells: Specifies the number of cells used to represent the size of an
+ address. Must be present if ranges is used.
+
+Example:
+
+foo@1000 {
+ compatible = "syscon", "simple-mfd";
+ reg = <0x01000 0x1000>;
+
+ led@8.0 {
+ compatible = "register-bit-led";
+ offset = <0x08>;
+ mask = <0x01>;
+ label = "myled";
+ default-state = "on";
+ };
+};