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| -rw-r--r-- | Documentation/ABI/testing/sysfs-firmware-ofw | 52 |
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diff --git a/Documentation/ABI/testing/sysfs-firmware-ofw b/Documentation/ABI/testing/sysfs-firmware-ofw new file mode 100644 index 000000000..edcab3ccf --- /dev/null +++ b/Documentation/ABI/testing/sysfs-firmware-ofw @@ -0,0 +1,52 @@ +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 |