Device tree basics

Typically, <.dtsi> file contain definitions of SoC-level information.

The <.dts> file contains board-level information.

Using device tree compiler

sudo apt install -y device-tree-compiler

Check nodes and properties

/proc/device-tree/ and / node of a device tree source(DTS) are the same.

If a DTS is

/ {
model = "A";
}

The structure of /proc/device-tree/ is as follows.

/proc/device-tree
โ””โ”€โ”€ model
cat /proc/device-tree
A

So, you can check DTS with one of the following commands.

tree /proc/device-tree
fdtdump <.dtb file name> | vim -

DTS modification

fdtget/fdtput

fdtget <.dtb> <node> <property>
fdtput -t <type> <.dtb> <node> <property> <value>
  • type
    • s=string, i=int, u=unsigned, x=hex
    • Optional modifier prefix: hh or b=byte, h=2 byte, l=4 byte (default)

Decompiled file modification

dtc -I dtb -O dts <.dtb> -o <.dts>

After decompiling with the above command, edit <.dts>. Then, compile the edited file with the below command.

dtc -I dts -O dtb <.dts> -o <.dtb>

Using Linux kernel source

git clone --depth=1 --branch=<branch> <repository>

After editing DTS, check Makefile.

linux/arch/<arch>/boot/dts/<vendor>/Makefile
dtb-$(CONFIG_ARCH_<BOARD>) += <board>.dtb

Then, execute the below commands.

make xxx_defconfig \
&& make dtbs

Then, DTB will be created in linux/arch/<arch>/boot/.

tip

If the above command fails, check arch/<arch>/configs. If not in arch/<arch>/configs, get a config file using zcat /proc/config.gz > <board>_defconfig from the kernel installed on the desired board.

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