1What:		/sys/firmware/devicetree/*
2Date:		November 2013
3Contact:	Grant Likely <grant.likely@arm.com>, devicetree@vger.kernel.org
4Description:
5		When using OpenFirmware or a Flattened Device Tree to enumerate
6		hardware, the device tree structure will be exposed in this
7		directory.
8
9		It is possible for multiple device-tree directories to exist.
10		Some device drivers use a separate detached device tree which
11		have no attachment to the system tree and will appear in a
12		different subdirectory under /sys/firmware/devicetree.
13
14		Userspace must not use the /sys/firmware/devicetree/base
15		path directly, but instead should follow /proc/device-tree
16		symlink. It is possible that the absolute path will change
17		in the future, but the symlink is the stable ABI.
18
19		The /proc/device-tree symlink replaces the devicetree /proc
20		filesystem support, and has largely the same semantics and
21		should be compatible with existing userspace.
22
23		The contents of /sys/firmware/devicetree/ is a
24		hierarchy of directories, one per device tree node. The
25		directory name is the resolved path component name (node
26		name plus address). Properties are represented as files
27		in the directory. The contents of each file is the exact
28		binary data from the device tree.
29
30What:		/sys/firmware/fdt
31Date:		February 2015
32KernelVersion:	3.19
33Contact:	Frank Rowand <frowand.list@gmail.com>, devicetree@vger.kernel.org
34Description:
35		Exports the FDT blob that was passed to the kernel by
36		the bootloader. This allows userland applications such
37		as kexec to access the raw binary. This blob is also
38		useful when debugging since it contains any changes
39		made to the blob by the bootloader.
40
41		The fact that this node does not reside under
42		/sys/firmware/device-tree is deliberate: FDT is also used
43		on arm64 UEFI/ACPI systems to communicate just the UEFI
44		and ACPI entry points, but the FDT is never unflattened
45		and used to configure the system.
46
47		A CRC32 checksum is calculated over the entire FDT
48		blob, and verified at late_initcall time. The sysfs
49		entry is instantiated only if the checksum is valid,
50		i.e., if the FDT blob has not been modified in the mean
51		time. Otherwise, a warning is printed.
52Users:		kexec, debugging
53