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