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Linux kernel mirror (for testing)
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linux
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
21 should consider all subnodes of the MFD device as separate and independent
22 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 for
24 a simple memory-mapped bus.
25 For more complex devices, when the nexus driver has to probe registers to
26 figure out what child devices exist etc, this should not be used. In the
27 latter case the child devices will be determined by the operating system.
28
29- ranges: Describes the address mapping relationship to the parent. Should set
30 the child's base address to 0, the physical address within parent's address
31 space, and the length of the address map.
32
33- #address-cells: Specifies the number of cells used to represent physical base
34 addresses. Must be present if ranges is used.
35
36- #size-cells: Specifies the number of cells used to represent the size of an
37 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};