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