1Common properties
2=================
3
4Endianness
5----------
6
7The Devicetree Specification does not define any properties related to hardware
8byte swapping, but endianness issues show up frequently in porting drivers to
9different machine types.  This document attempts to provide a consistent
10way of handling byte swapping across drivers.
11
12Optional properties:
13 - big-endian: Boolean; force big endian register accesses
14   unconditionally (e.g. ioread32be/iowrite32be).  Use this if you
15   know the peripheral always needs to be accessed in big endian (BE) mode.
16 - little-endian: Boolean; force little endian register accesses
17   unconditionally (e.g. readl/writel).  Use this if you know the
18   peripheral always needs to be accessed in little endian (LE) mode.
19 - native-endian: Boolean; always use register accesses matched to the
20   endianness of the kernel binary (e.g. LE vmlinux -> readl/writel,
21   BE vmlinux -> ioread32be/iowrite32be).  In this case no byte swaps
22   will ever be performed.  Use this if the hardware "self-adjusts"
23   register endianness based on the CPU's configured endianness.
24
25If a binding supports these properties, then the binding should also
26specify the default behavior if none of these properties are present.
27In such cases, little-endian is the preferred default, but it is not
28a requirement.  Some implementations assume that little-endian is
29the default, because most existing (PCI-based) drivers implicitly
30default to LE for their MMIO accesses.
31
32Examples:
33Scenario 1 : CPU in LE mode & device in LE mode.
34dev: dev@40031000 {
35	      compatible = "name";
36	      reg = <0x40031000 0x1000>;
37	      ...
38	      native-endian;
39};
40
41Scenario 2 : CPU in LE mode & device in BE mode.
42dev: dev@40031000 {
43	      compatible = "name";
44	      reg = <0x40031000 0x1000>;
45	      ...
46	      big-endian;
47};
48
49Scenario 3 : CPU in BE mode & device in BE mode.
50dev: dev@40031000 {
51	      compatible = "name";
52	      reg = <0x40031000 0x1000>;
53	      ...
54	      native-endian;
55};
56
57Scenario 4 : CPU in BE mode & device in LE mode.
58dev: dev@40031000 {
59	      compatible = "name";
60	      reg = <0x40031000 0x1000>;
61	      ...
62	      little-endian;
63};
64
65Daisy-chained devices
66---------------------
67
68Many serially-attached GPIO and IIO devices are daisy-chainable.  To the
69host controller, a daisy-chain appears as a single device, but the number
70of inputs and outputs it provides is the sum of inputs and outputs provided
71by all of its devices.  The driver needs to know how many devices the
72daisy-chain comprises to determine the amount of data exchanged, how many
73inputs and outputs to register and so on.
74
75Optional properties:
76 - #daisy-chained-devices: Number of devices in the daisy-chain (default is 1).
77
78Example:
79gpio@0 {
80	      compatible = "name";
81	      reg = <0>;
82	      gpio-controller;
83	      #gpio-cells = <2>;
84	      #daisy-chained-devices = <3>;
85};
86