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1Multi-Function Devices (MFD)2 3These devices comprise a nexus for heterogeneous hardware blocks containing4more 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 Management9 Integrated Circuit) that is manufactured in a lower technology node (rough10 silicon) that handles analog drivers for things like audio amplifiers, LED11 drivers, level shifters, PHY (physical interfaces to things like USB or12 ethernet), regulators etc.13 14- A range of memory registers containing "miscellaneous system registers" also15 known as a system controller "syscon" or any other memory range containing a16 mix of unrelated hardware devices.17 18Optional properties:19 20- compatible : "simple-mfd" - this signifies that the operating system21 should consider all subnodes of the MFD device as separate and independent22 devices, so not needing any resources to be provided by the parent device.23 Similarly to how "simple-bus" indicates when to see subnodes as children for24 a simple memory-mapped bus.25 For more complex devices, when the nexus driver has to probe registers to26 figure out what child devices exist etc, this should not be used. In the27 latter case the child devices will be determined by the operating system.28 29- ranges: Describes the address mapping relationship to the parent. Should set30 the child's base address to 0, the physical address within parent's address31 space, and the length of the address map.32 33- #address-cells: Specifies the number of cells used to represent physical base34 addresses. Must be present if ranges is used.35 36- #size-cells: Specifies the number of cells used to represent the size of an37 address. Must be present if ranges is used.38 39Example:40 41foo@1000 {42 compatible = "syscon", "simple-mfd";43 reg = <0x01000 0x1000>;44 45 led@8.0 {46 compatible = "register-bit-led";47 offset = <0x08>;48 mask = <0x01>;49 label = "myled";50 default-state = "on";51 };52};53