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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/devicetree/bindings/chosen.txt | |
parent | Initial commit. (diff) | |
download | linux-430c2fc249ea5c0536abd21c23382884005c9093.tar.xz linux-430c2fc249ea5c0536abd21c23382884005c9093.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/devicetree/bindings/chosen.txt')
-rw-r--r-- | Documentation/devicetree/bindings/chosen.txt | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt new file mode 100644 index 000000000..45e79172a --- /dev/null +++ b/Documentation/devicetree/bindings/chosen.txt @@ -0,0 +1,137 @@ +The chosen node +--------------- + +The chosen node does not represent a real device, but serves as a place +for passing data between firmware and the operating system, like boot +arguments. Data in the chosen node does not represent the hardware. + +The following properties are recognized: + + +kaslr-seed +----------- + +This property is used when booting with CONFIG_RANDOMIZE_BASE as the +entropy used to randomize the kernel image base address location. Since +it is used directly, this value is intended only for KASLR, and should +not be used for other purposes (as it may leak information about KASLR +offsets). It is parsed as a u64 value, e.g. + +/ { + chosen { + kaslr-seed = <0xfeedbeef 0xc0def00d>; + }; +}; + +Note that if this property is set from UEFI (or a bootloader in EFI +mode) when EFI_RNG_PROTOCOL is supported, it will be overwritten by +the Linux EFI stub (which will populate the property itself, using +EFI_RNG_PROTOCOL). + +stdout-path +----------- + +Device trees may specify the device to be used for boot console output +with a stdout-path property under /chosen, as described in the Devicetree +Specification, e.g. + +/ { + chosen { + stdout-path = "/serial@f00:115200"; + }; + + serial@f00 { + compatible = "vendor,some-uart"; + reg = <0xf00 0x10>; + }; +}; + +If the character ":" is present in the value, this terminates the path. +The meaning of any characters following the ":" is device-specific, and +must be specified in the relevant binding documentation. + +For UART devices, the preferred binding is a string in the form: + + <baud>{<parity>{<bits>{<flow>}}} + +where + + baud - baud rate in decimal + parity - 'n' (none), 'o', (odd) or 'e' (even) + bits - number of data bits + flow - 'r' (rts) + +For example: 115200n8r + +Implementation note: Linux will look for the property "linux,stdout-path" or +on PowerPC "stdout" if "stdout-path" is not found. However, the +"linux,stdout-path" and "stdout" properties are deprecated. New platforms +should only use the "stdout-path" property. + +linux,booted-from-kexec +----------------------- + +This property is set (currently only on PowerPC, and only needed on +book3e) by some versions of kexec-tools to tell the new kernel that it +is being booted by kexec, as the booting environment may differ (e.g. +a different secondary CPU release mechanism) + +linux,usable-memory-range +------------------------- + +This property (arm64 only) holds a base address and size, describing a +limited region in which memory may be considered available for use by +the kernel. Memory outside of this range is not available for use. + +This property describes a limitation: memory within this range is only +valid when also described through another mechanism that the kernel +would otherwise use to determine available memory (e.g. memory nodes +or the EFI memory map). Valid memory may be sparse within the range. +e.g. + +/ { + chosen { + linux,usable-memory-range = <0x9 0xf0000000 0x0 0x10000000>; + }; +}; + +The main usage is for crash dump kernel to identify its own usable +memory and exclude, at its boot time, any other memory areas that are +part of the panicked kernel's memory. + +While this property does not represent a real hardware, the address +and the size are expressed in #address-cells and #size-cells, +respectively, of the root node. + +linux,elfcorehdr +---------------- + +This property (currently used only on arm64) holds the memory range, +the address and the size, of the elf core header which mainly describes +the panicked kernel's memory layout as PT_LOAD segments of elf format. +e.g. + +/ { + chosen { + linux,elfcorehdr = <0x9 0xfffff000 0x0 0x800>; + }; +}; + +While this property does not represent a real hardware, the address +and the size are expressed in #address-cells and #size-cells, +respectively, of the root node. + +linux,initrd-start and linux,initrd-end +--------------------------------------- + +These properties hold the physical start and end address of an initrd that's +loaded by the bootloader. Note that linux,initrd-start is inclusive, but +linux,initrd-end is exclusive. +e.g. + +/ { + chosen { + linux,initrd-start = <0x82000000>; + linux,initrd-end = <0x82800000>; + }; +}; |