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Diffstat (limited to 'Documentation/devicetree/bindings/common-properties.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/common-properties.txt | 17 |
1 files changed, 8 insertions, 9 deletions
diff --git a/Documentation/devicetree/bindings/common-properties.txt b/Documentation/devicetree/bindings/common-properties.txt index a3448bfa1c82..98a28130e100 100644 --- a/Documentation/devicetree/bindings/common-properties.txt +++ b/Documentation/devicetree/bindings/common-properties.txt @@ -5,30 +5,29 @@ Endianness ---------- The Devicetree Specification does not define any properties related to hardware -byteswapping, but endianness issues show up frequently in porting Linux to +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 byteswapping across drivers. +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 BE mode. + 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 LE mode. + 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 byteswaps + 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. 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. +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. |