Add the rt linux 4.1.3-rt3 as base

[kvmfornfv.git] / kernel / Documentation / devicetree / bindings / common-properties.txt

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+Common properties
+
+The ePAPR specification does not define any properties related to hardware
+byteswapping, but endianness issues show up frequently in porting Linux to
+different machine types.  This document attempts to provide a consistent
+way of handling byteswapping across drivers.
+
+Optional properties:
+ - big-endian: Boolean; force big endian register accesses
+   unconditionally (e.g. ioread32be/iowrite32be).  Use this if you
+   know the peripheral always needs to be accessed in BE mode.
+ - little-endian: Boolean; force little endian register accesses
+   unconditionally (e.g. readl/writel).  Use this if you know the
+   peripheral always needs to be accessed in LE mode.
+ - native-endian: Boolean; always use register accesses matched to the
+   endianness of the kernel binary (e.g. LE vmlinux -> readl/writel,
+   BE vmlinux -> ioread32be/iowrite32be).  In this case no byteswaps
+   will ever be performed.  Use this if the hardware "self-adjusts"
+   register endianness based on the CPU's configured endianness.
+
+If a binding supports these properties, then the binding should also
+specify the default behavior if none of these properties are present.
+In such cases, little-endian is the preferred default, but it is not
+a requirement.  The of_device_is_big_endian() and of_fdt_is_big_endian()
+helper functions do assume that little-endian is the default, because
+most existing (PCI-based) drivers implicitly default to LE by using
+readl/writel for MMIO accesses.
+
+Examples:
+Scenario 1 : CPU in LE mode & device in LE mode.
+dev: dev@40031000 {
+             compatible = "name";
+             reg = <0x40031000 0x1000>;
+             ...
+             native-endian;
+};
+
+Scenario 2 : CPU in LE mode & device in BE mode.
+dev: dev@40031000 {
+             compatible = "name";
+             reg = <0x40031000 0x1000>;
+             ...
+             big-endian;
+};
+
+Scenario 3 : CPU in BE mode & device in BE mode.
+dev: dev@40031000 {
+             compatible = "name";
+             reg = <0x40031000 0x1000>;
+             ...
+             native-endian;
+};
+
+Scenario 4 : CPU in BE mode & device in LE mode.
+dev: dev@40031000 {
+             compatible = "name";
+             reg = <0x40031000 0x1000>;
+             ...
+             little-endian;
+};