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