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What: /sys/firmware/devicetree/*
Date: November 2013
Contact: Grant Likely <grant.likely@arm.com>, devicetree@vger.kernel.org
Description:
When using OpenFirmware or a Flattened Device Tree to enumerate
hardware, the device tree structure will be exposed in this
directory.
It is possible for multiple device-tree directories to exist.
Some device drivers use a separate detached device tree which
have no attachment to the system tree and will appear in a
different subdirectory under /sys/firmware/devicetree.
Userspace must not use the /sys/firmware/devicetree/base
path directly, but instead should follow /proc/device-tree
symlink. It is possible that the absolute path will change
in the future, but the symlink is the stable ABI.
The /proc/device-tree symlink replaces the devicetree /proc
filesystem support, and has largely the same semantics and
should be compatible with existing userspace.
The contents of /sys/firmware/devicetree/ is a
hierarchy of directories, one per device tree node. The
directory name is the resolved path component name (node
name plus address). Properties are represented as files
in the directory. The contents of each file is the exact
binary data from the device tree.
What: /sys/firmware/fdt
Date: February 2015
KernelVersion: 3.19
Contact: Frank Rowand <frowand.list@gmail.com>, devicetree@vger.kernel.org
Description:
Exports the FDT blob that was passed to the kernel by
the bootloader. This allows userland applications such
as kexec to access the raw binary. This blob is also
useful when debugging since it contains any changes
made to the blob by the bootloader.
The fact that this node does not reside under
/sys/firmware/device-tree is deliberate: FDT is also used
on arm64 UEFI/ACPI systems to communicate just the UEFI
and ACPI entry points, but the FDT is never unflattened
and used to configure the system.
A CRC32 checksum is calculated over the entire FDT
blob, and verified at late_initcall time. The sysfs
entry is instantiated only if the checksum is valid,
i.e., if the FDT blob has not been modified in the mean
time. Otherwise, a warning is printed.
Users: kexec, debugging
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