1 Common properties
2 =================
3
4 Endianness
5 ----------
6
7 The Devicetree Specification does not define a
8 byte swapping, but endianness issues show up f
9 different machine types. This document attemp
10 way of handling byte swapping across drivers.
11
12 Optional properties:
13 - big-endian: Boolean; force big endian regis
14 unconditionally (e.g. ioread32be/iowrite32b
15 know the peripheral always needs to be acce
16 - little-endian: Boolean; force little endian
17 unconditionally (e.g. readl/writel). Use t
18 peripheral always needs to be accessed in l
19 - native-endian: Boolean; always use register
20 endianness of the kernel binary (e.g. LE vm
21 BE vmlinux -> ioread32be/iowrite32be). In
22 will ever be performed. Use this if the ha
23 register endianness based on the CPU's conf
24
25 If a binding supports these properties, then t
26 specify the default behavior if none of these
27 In such cases, little-endian is the preferred
28 a requirement. Some implementations assume th
29 the default, because most existing (PCI-based)
30 default to LE for their MMIO accesses.
31
32 Examples:
33 Scenario 1 : CPU in LE mode & device in LE mod
34 dev: dev@40031000 {
35 compatible = "name";
36 reg = <0x40031000 0x1000>;
37 ...
38 native-endian;
39 };
40
41 Scenario 2 : CPU in LE mode & device in BE mod
42 dev: dev@40031000 {
43 compatible = "name";
44 reg = <0x40031000 0x1000>;
45 ...
46 big-endian;
47 };
48
49 Scenario 3 : CPU in BE mode & device in BE mod
50 dev: dev@40031000 {
51 compatible = "name";
52 reg = <0x40031000 0x1000>;
53 ...
54 native-endian;
55 };
56
57 Scenario 4 : CPU in BE mode & device in LE mod
58 dev: dev@40031000 {
59 compatible = "name";
60 reg = <0x40031000 0x1000>;
61 ...
62 little-endian;
63 };
64
65 Daisy-chained devices
66 ---------------------
67
68 Many serially-attached GPIO and IIO devices ar
69 host controller, a daisy-chain appears as a si
70 of inputs and outputs it provides is the sum o
71 by all of its devices. The driver needs to kn
72 daisy-chain comprises to determine the amount
73 inputs and outputs to register and so on.
74
75 Optional properties:
76 - #daisy-chained-devices: Number of devices i
77
78 Example:
79 gpio@0 {
80 compatible = "name";
81 reg = <0>;
82 gpio-controller;
83 #gpio-cells = <2>;
84 #daisy-chained-devices = <3>;
85 };
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