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Subject[PATCH V4 3/5] of: Document {little,big,native}-endian bindings
Date
These apply to newly converted drivers, like serial8250/libahci/...
The examples were adapted from the regmap bindings document.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
---
.../devicetree/bindings/common-properties.txt | 60 ++++++++++++++++++++++
1 file changed, 60 insertions(+)
create mode 100644 Documentation/devicetree/bindings/common-properties.txt

diff --git a/Documentation/devicetree/bindings/common-properties.txt b/Documentation/devicetree/bindings/common-properties.txt
new file mode 100644
index 000000000000..3193979b1d05
--- /dev/null
+++ b/Documentation/devicetree/bindings/common-properties.txt
@@ -0,0 +1,60 @@
+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;
+};
--
2.2.2


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