1Multi-Function Devices (MFD) 2 3These devices comprise a nexus for heterogeneous hardware blocks containing 4more than one non-unique yet varying hardware functionality. 5 6A typical MFD can be: 7 8- A mixed signal ASIC on an external bus, sometimes a PMIC (Power Management 9 Integrated Circuit) that is manufactured in a lower technology node (rough 10 silicon) that handles analog drivers for things like audio amplifiers, LED 11 drivers, level shifters, PHY (physical interfaces to things like USB or 12 ethernet), regulators etc. 13 14- A range of memory registers containing "miscellaneous system registers" also 15 known as a system controller "syscon" or any other memory range containing a 16 mix of unrelated hardware devices. 17 18Optional properties: 19 20- compatible : "simple-mfd" - this signifies that the operating system should 21 consider all subnodes of the MFD device as separate devices akin to how 22 "simple-bus" indicates when to see subnodes as children for a simple 23 memory-mapped bus. For more complex devices, when the nexus driver has to 24 probe registers to figure out what child devices exist etc, this should not 25 be used. In the latter case the child devices will be determined by the 26 operating system. 27 28- ranges: Describes the address mapping relationship to the parent. Should set 29 the child's base address to 0, the physical address within parent's address 30 space, and the length of the address map. 31 32- #address-cells: Specifies the number of cells used to represent physical base 33 addresses. Must be present if ranges is used. 34 35- #size-cells: Specifies the number of cells used to represent the size of an 36 address. Must be present if ranges is used. 37 38Example: 39 40foo@1000 { 41 compatible = "syscon", "simple-mfd"; 42 reg = <0x01000 0x1000>; 43 44 led@08.0 { 45 compatible = "register-bit-led"; 46 offset = <0x08>; 47 mask = <0x01>; 48 label = "myled"; 49 default-state = "on"; 50 }; 51}; 52