1Common properties
2
3The ePAPR specification does not define any properties related to hardware
4byteswapping, but endianness issues show up frequently in porting Linux to
5different machine types.  This document attempts to provide a consistent
6way of handling byteswapping across drivers.
7
8Optional properties:
9 - big-endian: Boolean; force big endian register accesses
10   unconditionally (e.g. ioread32be/iowrite32be).  Use this if you
11   know the peripheral always needs to be accessed in BE mode.
12 - little-endian: Boolean; force little endian register accesses
13   unconditionally (e.g. readl/writel).  Use this if you know the
14   peripheral always needs to be accessed in LE mode.
15 - native-endian: Boolean; always use register accesses matched to the
16   endianness of the kernel binary (e.g. LE vmlinux -> readl/writel,
17   BE vmlinux -> ioread32be/iowrite32be).  In this case no byteswaps
18   will ever be performed.  Use this if the hardware "self-adjusts"
19   register endianness based on the CPU's configured endianness.
20
21If a binding supports these properties, then the binding should also
22specify the default behavior if none of these properties are present.
23In such cases, little-endian is the preferred default, but it is not
24a requirement.  The of_device_is_big_endian() and of_fdt_is_big_endian()
25helper functions do assume that little-endian is the default, because
26most existing (PCI-based) drivers implicitly default to LE by using
27readl/writel for MMIO accesses.
28
29Examples:
30Scenario 1 : CPU in LE mode & device in LE mode.
31dev: dev@40031000 {
32	      compatible = "name";
33	      reg = <0x40031000 0x1000>;
34	      ...
35	      native-endian;
36};
37
38Scenario 2 : CPU in LE mode & device in BE mode.
39dev: dev@40031000 {
40	      compatible = "name";
41	      reg = <0x40031000 0x1000>;
42	      ...
43	      big-endian;
44};
45
46Scenario 3 : CPU in BE mode & device in BE mode.
47dev: dev@40031000 {
48	      compatible = "name";
49	      reg = <0x40031000 0x1000>;
50	      ...
51	      native-endian;
52};
53
54Scenario 4 : CPU in BE mode & device in LE mode.
55dev: dev@40031000 {
56	      compatible = "name";
57	      reg = <0x40031000 0x1000>;
58	      ...
59	      little-endian;
60};
61