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Commit 65a71007 authored by Kevin Cernekee's avatar Kevin Cernekee Committed by Rob Herring
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of: Document {little,big,native}-endian bindings 



These apply to newly converted drivers, like serial8250/libahci/...
The examples were adapted from the regmap bindings document.

Signed-off-by: default avatarKevin Cernekee <cernekee@gmail.com>
Reviewed-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarRob Herring <robh@kernel.org>
parent cc783786

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;

};