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.. SPDX-License-Identifier: GPL-2.0+ .. index:: single: fdt (command) fdt command =========== Synopsis -------- :: fdt addr [-cq] [addr [len]] fdt reserved Description ----------- The fdt command provides access to flat device tree blobs in memory. It has many subcommands, some of which are not documented here. Flags: -c Select the control FDT (otherwise the working FDT is used). -q Don't display errors The control FDT is the one used by U-Boot itself to control various features, including driver model. This should only be changed if you really know what you are doing, since once U-Boot starts it maintains pointers into the FDT from the various driver model data structures. The working FDT is the one passed to the Operating System when booting. This can be freely modified, so far as U-Boot is concerned, since it does not affect U-Boot's operation. fdt addr ~~~~~~~~ With no arguments, this shows the address of the current working or control FDT. If the `addr` argument is provided, then this sets the address of the working or control FDT to the provided address. If the `len` argument is provided, then the device tree is expanded to that size. This can be used to make space for more nodes and properties. It is assumed that there is enough space in memory for this expansion. fdt reserved ~~~~~~~~~~~~ This command prints all reserved memory regions defined in the device tree's `/reserved-memory` node. The output shows a formatted table with the following columns: - **ID**: Sequential number for each region - **Name**: Node name of the reserved memory region - **Start**: Start address of the reserved memory region in hexadecimal - **Size**: Size of the reserved memory region in hexadecimal If no `/reserved-memory` node exists in the device tree, the command will display an appropriate message. This command is useful for debugging memory layout issues and verifying that reserved memory regions are properly defined. This subcommand is only present is `CONFIG_CMD_FDT_RESERVED` is enabled. Example ------- Get the control address and copy that FDT to free memory:: => fdt addr -c Control fdt: 0aff9fd0 => cp.b 0aff9fd0 10000 10000 => md 10000 4 00010000: edfe0dd0 5b3d0000 78000000 7c270000 ......=[...x..'| The second word shows the size of the FDT. Now set the working FDT to that address and expand it to 0xf000 in size:: => fdt addr 10000 f000 Working FDT set to 10000 => md 10000 4 00010000: edfe0dd0 00f00000 78000000 7c270000 ...........x..'| Print all reserved memory regions:: => fdt reserved ID Name Start Size ---------------------------------------------------------------- 0 secmon@1f000000 0x000000001f000000 0x0000000001000000 1 atf@40000000 0x0000000040000000 0x0000000000200000 2 linux,cma 0x0000000050000000 0x0000000008000000 Return value ------------ The return value $? indicates whether the command succeeded. |