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fix: Update the how_to_check_device_tree_info guide
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Fix the examples in this guide by implementing the following:
- Switch from xxd to hexdump since xxd is no longer packaged in fs
- Add examples and logs for am62* devices
- Update code blocks to .. code-block:: console format
- Make the document more generic by using <machine> for device in logs

Signed-off-by: Judith Mendez <[email protected]>
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@jmenti
jmenti committed Dec 10, 2024
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191 changes: 131 additions & 60 deletions source/linux/How_to_Guides/FAQ/How_to_Check_Device_Tree_Info.rst
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Expand Up @@ -9,81 +9,152 @@ using the entries in /proc/device-tree.
In the command prompt of Linux, you should see something similar to the
following in the /proc/device-tree directory:

::

root@j721e-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
.. code-block:: console
root@<machine>:~# 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
Following are some typical usages you might need:

- Let's say you don't know the exact path of the device tree entry you are
trying to check. 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. You can find the exact path for that symbol by running ``cat``
command on that entry. Following is an example demonstrating the use:
Let's say you don't know the exact path of the device tree entry you are
trying to check. 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. You can find the exact path for that symbol by running ``cat``
command on that entry. Following is an example demonstrating the use:

::
.. ifconfig:: CONFIG_part_variant not in ('AM62X', 'AM62PX', 'AM62AX', 'AM64X', 'AM65X')

root@j721e-evm:~# cat /proc/device-tree/__symbols__/main_i2c0
/interconnect@100000/i2c@2000000
.. code-block:: console
root@j721e-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
root@<machine>:~# cat /proc/device-tree/__symbols__/main_i2c0
/interconnect@100000/i2c@2000000
- You can check the value of a device tree entry using ``cat`` command if it is a
string. But if the value is an integer or some numeric data, you will have to
run the ``xxd`` command instead of ``cat``, to get output in a readable format.
Following is an example demonstrating the use:
root@<machine>:~# 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
::
.. ifconfig:: CONFIG_part_variant in ('AM62X', 'AM62PX', 'AM62AX', 'AM64X', 'AM65X')

# Example for a string value
root@j721e-evm:~# cat /proc/device-tree/interconnect@100000/i2c@2000000/compatible
ti,j721e-i2cti,omap4-i2c
.. code-block:: console
# Example for an integer value
root@j721e-evm:~# xxd -g4 /proc/device-tree/interconnect@100000/i2c@2000000/clock-frequency
00000000: 00061a80 ....
root@<machine>:~# cat /proc/device-tree/__symbols__/main_i2c0
/bus@<address>/i2c@20000000
# The above value is in hexadecimal. You can calculate it's value in decimal by using following command
root@j721e-evm:~# echo $((0x00061a80))
400000
root@<machine>:~# ls /proc/device-tree/bus@<address>/i2c@20000000/
'#address-cells' clock-names eeprom@51 phandle power-domains tps6598x@3f
'#size-cells' clocks interrupts pinctrl-0 reg
clock-frequency compatible name pinctrl-names status
- 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 following for the specific processor core.
You can check the value of a device tree entry using ``cat`` command if it is a
string. But if the value is an integer or some numeric data, you will have to
run the ``hexdump`` command instead of ``cat``, to get output in a readable format.
Following is an example demonstrating the use:

::
.. ifconfig:: CONFIG_part_variant not in ('AM62X', 'AM62PX', 'AM62AX', 'AM64X', 'AM65X')

# Finding symbols for R5Fs
root@j721e-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
.. code-block:: console
# Finding location from the symbols
root@j721e-evm:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_memory_region
/reserved-memory/r5f-memory@a2100000
# Example for a string value
root@<machine>:~# cat /proc/device-tree/interconnect@100000/i2c@2000000/compatible
ti,j721e-i2cti,omap4-i2c
root@j721e-evm:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_dma_memory_region
/reserved-memory/r5f-dma-memory@a2000000
# Example for an integer value where the first column represents input offsets
root@<machine>:~# hexdump -C /proc/device-tree/interconnect@100000/i2c@2000000/clock-frequency
00000000 00 06 1a 80 |....|
00000004
# Checking the values
root@j721e-evm:~# xxd -g4 /proc/device-tree/reserved-memory/r5f-memory@a2100000/reg
00000000: 00000000 a2100000 00000000 01f00000 ................
# The above value is in hexadecimal. You can calculate it's value in decimal by using following command
root@<machine>:~# echo $((0x00061a80))
400000
root@j721e-evm:~# xxd -g4 /proc/device-tree/reserved-memory/r5f-dma-memory@a2000000/reg
00000000: 00000000 a2000000 00000000 00100000 ................
.. ifconfig:: CONFIG_part_variant in ('AM62X', 'AM62PX', 'AM62AX', 'AM64X', 'AM65X')

.. code-block:: console
# Example for a string value
root@<machine>:~# cat /proc/device-tree/bus@<address>/i2c@20000000/compatible
ti,am64-i2cti,omap4-i2c
# Example for an integer value where the first column represents input offsets
root@<machine>:~# hexdump -C /proc/device-tree/bus@<address>/i2c@20000000/clock-frequency
00000000 00 06 1a 80 |....|
00000004
# The above value is in hexadecimal. You can calculate it's value in decimal by using following command
root@<machine>:~# echo $((0x00061a80))
400000
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 following for the specific processor core.

.. ifconfig:: CONFIG_part_variant not in ('AM62X', 'AM62PX', 'AM62AX', 'AM64X', 'AM65X')

.. code-block:: console
# Finding symbols for R5Fs
root@<machine>:~# 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 location from the symbols
root@<machine>:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_memory_region
/reserved-memory/r5f-memory@a2100000
root@<machine>:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_dma_memory_region
/reserved-memory/r5f-dma-memory@a2000000
# Checking the values
root@<machine>:~# hexdump -C /proc/device-tree/reserved-memory/r5f-memory@a2100000/reg
00000000: 00000000 a2100000 00000000 01<address>0 ................
root@<machine>:~# hexdump -C /proc/device-tree/reserved-memory/r5f-dma-memory@a2000000/reg
00000000: 00000000 a2000000 00000000 00100000 ................
.. ifconfig:: CONFIG_part_variant in ('AM62X', 'AM62PX', 'AM62AX', 'AM64X', 'AM65X')

.. code-block:: console
# Finding symbols for remote cores
root@<machine>:~# ls /proc/device-tree/__symbols__/ | grep "r5f"; ls /proc/device-tree/__symbols__/ | grep "m4f"; ls /proc/device-tree/__symbols__/ | grep "c7x";
wkup_r5fss0
wkup_r5fss0_core0
wkup_r5fss0_core0_dma_memory_region
wkup_r5fss0_core0_memory_region
mcu_m4fss
mcu_m4fss_dma_memory_region
mcu_m4fss_memory_region
# Finding location from the symbols
root@<machine>:~# cat /proc/device-tree/__symbols__/mcu_m4fss_memory_region
/reserved-memory/m4f-memory@9cc00000
root@<machine>:~# cat /proc/device-tree/__symbols__/mcu_m4fss_dma_memory_region
/reserved-memory/m4f-dma-memory@9cb00000
# Checking the values
root@<machine>:~# hexdump -C /proc/device-tree/reserved-memory/m4f-memory@9cc00000/reg
00000000 00 00 00 00 9c c0 00 00 00 00 00 00 00 e0 00 00 |................|
00000010
root@<machine>:~# hexdump -C /proc/device-tree/reserved-memory/m4f-dma-memory@9cb00000/reg
00000000 00 00 00 00 9c b0 00 00 00 00 00 00 00 10 00 00 |................|
00000010
.. warning::

**IMPORTANT**: Before tweaking the memory for remote processors, please verify that the memory
can be modified since some remote processors can be running firmware like DM firmware.

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