Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 85 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/common-properties.txt b/Documentation/devicetree/bindings/common-properties.txt
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+Common properties
+=================
+
+Endianness
+----------
+
+The Devicetree Specification does not define any properties related to hardware
+byte swapping, but endianness issues show up frequently in porting drivers to
+different machine types.  This document attempts to provide a consistent
+way of handling byte swapping 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 big endian (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 little endian (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 byte swaps
+   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.  Some implementations assume that little-endian is
+the default, because most existing (PCI-based) drivers implicitly
+default to LE for their 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;
+};
+
+Daisy-chained devices
+---------------------
+
+Many serially-attached GPIO and IIO devices are daisy-chainable.  To the
+host controller, a daisy-chain appears as a single device, but the number
+of inputs and outputs it provides is the sum of inputs and outputs provided
+by all of its devices.  The driver needs to know how many devices the
+daisy-chain comprises to determine the amount of data exchanged, how many
+inputs and outputs to register and so on.
+
+Optional properties:
+ - #daisy-chained-devices: Number of devices in the daisy-chain (default is 1).
+
+Example:
+gpio@0 {
+	      compatible = "name";
+	      reg = <0>;
+	      gpio-controller;
+	      #gpio-cells = <2>;
+	      #daisy-chained-devices = <3>;
+};