Access device tree information from User Space

Revision History

Version Description of Changes Date
1.0 Initial Version 10/21/2022


The value of some dtb entry might have to be checked for debugging, or to verify that the dtb really got updated after it was modified, etc. Although a .dts-file-like view of the device tree which was loaded cannot be achieved, values can be verified using the entries on the in /proc/device-tree.

Something similar to the following can be seen on the command prompt in Linux in the /proc/device-tree directory:

root@j7-evm:~# ls /proc/device-tree/
#address-cells  firmware                l3-cache0
#size-cells     fixedregulator-evm12v0  main_r5fss_cpsw9g_virt_mac0
__symbols__     fixedregulator-sd       memory@80000000
aliases         fixedregulator-vsys3v3  model
chosen          fixedregulator-vsys5v0  name
compatible      gpio-keys               pmu
connector       interconnect@100000     reserved-memory
cpus            interrupt-parent        serial-number
dma_buf_phys    ion                     sound@0
dummy-panel     l2-cache0               timer-cl0-cpu0

Typical usage examples

  • If the exact path of the device tree entry to check is not known. There is a symbol directory in /proc/device-tree, which is very helpful in such cases. It has an entry for each symbol label in the device tree. The exact path for a symbol can be found by running the cat command on an entry. Following is an example demonstrating the use:

    root@j7-evm:~# cat /proc/device-tree/__symbols__/main_i2c0
    root@j7-evm:~# ls /proc/device-tree/interconnect@100000/i2c@2000000/
    #address-cells   clock-names  gpio@20     name       pinctrl-names
    #size-cells      clocks       gpio@22     phandle    power-domains
    clock-frequency  compatible   interrupts  pinctrl-0  reg
  • The value of a device tree entry can be checked using the cat command if it is a string. If the value is an integer or some numeric data, however, the xxd command will have to be used instead of cat, to get output in a readable format. Following is an example demonstrating the use:

    # Example for a string value
    root@j7-evm:~# cat /proc/device-tree/interconnect@100000/i2c@2000000/compatible
    # Example for an integer value
    root@j7-evm:~# xxd -g4 /proc/device-tree/interconnect@100000/i2c@2000000/clock-frequency
    00000000: 00061a80                             ....
    # The above value is in hexadecimal. You can calculate its value in decimal by using the following command
    root@j7-evm:~# echo $((0x00061a80))
  • One common scenario of a device tree change is tweaking the memory for remoteproc processors like R5F. You can check if it got updated correctly, by running a command similar to the following for the specific processor core.

    # Finding symbols for R5Fs
    root@j7-evm:~# ls /proc/device-tree/__symbols__/main_r5fss*
    /proc/device-tree/__symbols__/main_r5fss0                          /proc/device-tree/__symbols__/main_r5fss0_core1_dma_memory_region  /proc/device-tree/__symbols__/main_r5fss1_core0_memory_region
    /proc/device-tree/__symbols__/main_r5fss0_core0                    /proc/device-tree/__symbols__/main_r5fss0_core1_memory_region      /proc/device-tree/__symbols__/main_r5fss1_core1
    /proc/device-tree/__symbols__/main_r5fss0_core0_dma_memory_region  /proc/device-tree/__symbols__/main_r5fss1                          /proc/device-tree/__symbols__/main_r5fss1_core1_dma_memory_region
    /proc/device-tree/__symbols__/main_r5fss0_core0_memory_region      /proc/device-tree/__symbols__/main_r5fss1_core0                    /proc/device-tree/__symbols__/main_r5fss1_core1_memory_region
    /proc/device-tree/__symbols__/main_r5fss0_core1                    /proc/device-tree/__symbols__/main_r5fss1_core0_dma_memory_region
    # Finding the location from the symbols
    root@j7-evm:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_memory_region
    root@j7-evm:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_dma_memory_region
    # Checking the values
    root@j7-evm:~# xxd -g4 /proc/device-tree/reserved-memory/r5f-memory@a2100000/reg
    00000000: 00000000 a2100000 00000000 01f00000  ................
    root@j7-evm:~# xxd -g4 /proc/device-tree/reserved-memory/r5f-dma-memory@a2000000/reg
    00000000: 00000000 a2000000 00000000 00100000  ................