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