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1Common properties2=================3 4Endianness5----------6 7The Devicetree Specification does not define any properties related to hardware8byte swapping, but endianness issues show up frequently in porting drivers to9different machine types. This document attempts to provide a consistent10way of handling byte swapping across drivers.11 12Optional properties:13 - big-endian: Boolean; force big endian register accesses14 unconditionally (e.g. ioread32be/iowrite32be). Use this if you15 know the peripheral always needs to be accessed in big endian (BE) mode.16 - little-endian: Boolean; force little endian register accesses17 unconditionally (e.g. readl/writel). Use this if you know the18 peripheral always needs to be accessed in little endian (LE) mode.19 - native-endian: Boolean; always use register accesses matched to the20 endianness of the kernel binary (e.g. LE vmlinux -> readl/writel,21 BE vmlinux -> ioread32be/iowrite32be). In this case no byte swaps22 will ever be performed. Use this if the hardware "self-adjusts"23 register endianness based on the CPU's configured endianness.24 25If a binding supports these properties, then the binding should also26specify the default behavior if none of these properties are present.27In such cases, little-endian is the preferred default, but it is not28a requirement. Some implementations assume that little-endian is29the default, because most existing (PCI-based) drivers implicitly30default to LE for their MMIO accesses.31 32Examples:33Scenario 1 : CPU in LE mode & device in LE mode.34dev: dev@40031000 {35 compatible = "name";36 reg = <0x40031000 0x1000>;37 ...38 native-endian;39};40 41Scenario 2 : CPU in LE mode & device in BE mode.42dev: dev@40031000 {43 compatible = "name";44 reg = <0x40031000 0x1000>;45 ...46 big-endian;47};48 49Scenario 3 : CPU in BE mode & device in BE mode.50dev: dev@40031000 {51 compatible = "name";52 reg = <0x40031000 0x1000>;53 ...54 native-endian;55};56 57Scenario 4 : CPU in BE mode & device in LE mode.58dev: dev@40031000 {59 compatible = "name";60 reg = <0x40031000 0x1000>;61 ...62 little-endian;63};64 65Daisy-chained devices66---------------------67 68Many serially-attached GPIO and IIO devices are daisy-chainable. To the69host controller, a daisy-chain appears as a single device, but the number70of inputs and outputs it provides is the sum of inputs and outputs provided71by all of its devices. The driver needs to know how many devices the72daisy-chain comprises to determine the amount of data exchanged, how many73inputs and outputs to register and so on.74 75Optional properties:76 - #daisy-chained-devices: Number of devices in the daisy-chain (default is 1).77 78Example:79gpio@0 {80 compatible = "name";81 reg = <0>;82 gpio-controller;83 #gpio-cells = <2>;84 #daisy-chained-devices = <3>;85};86