Devicetree Compiler

Introduction to the DTC

Device Tree Compiler, dtc, takes as input a device-tree in a given format and outputs a device-tree in another format for booting kernels on embedded systems. Typically, the input format is "dts" (device-tree source), a human readable source format, and creates a "dtb" (device-tree binary), or binary format as output.

If the dtc tool is not installed on your host system, the dtc module will guide you through the installation.

Generate DTS

When you have a DTB or FDT file from firmware or another runtime system, you might want to convert it into a DTS file for easier reading. You can do this in Python or your SConscript file. For example, assuming you have dummpy.dtb:

import os, sys
 
RTT_ROOT = os.getenv('RTT_ROOT')
sys.path.append(RTT_ROOT + '/tools')
 
from building import *
import dtc
 
dtc.dtb_to_dts(RTT_ROOT, "dummpy.dtb")

This will generate a dummpy.dts in the current directory. If a file with the same name already exists, it will be replaced. To avoid overwriting, you can specify a different output name:

[...]
 
dtc.dtb_to_dts(RTT_ROOT, "dummpy.dtb", "dummpy-tmp.dts")
# or
dtc.dtb_to_dts(RTT_ROOT, "dummpy.dtb", dts_name = "dummpy-tmp.dts")

Generate DTB

Before generating a DTB, you may want to review the basics of DTS syntax and structure: DeviceTree Specification

Include and Macros

By default, dtc does not support C-style preprocessing (like cpp), but you can use the C preprocessor with your DTS files. Don't worry — our dtc module already includes this step.

If your DTS file uses dt-bindings headers or macros, you can write something like:

/*
 * Used "#include" if header file need preprocessor,
 * `components/drivers/include` and current directory path is default.
 */
#include <dt-bindings/size.h>
#include "dummy.dtsi"
/* Well, if dtsi is simple, you can use "/include/", it is supported by dtc */
/include/ "chosen.dtsi"
 
#define MMIO_BASE   0x10000
#define MMIO_SIZE   SIZE_GB
#define MEM_BASE    (MMIO_BASE + MMIO_SIZE)
 
#ifndef CPU_HARDID
#define CPU_HARDID  0
#endif
 
#ifndef SOC_INTC
#define SOC_INTC    intc_a
#endif
 
/ {
    #address-cells = <2>;
    #size-cells = <2>;
    /*
     * Macros after "&" will be replaced,
     * there will affect the interrupt controller in this SoC.
     */
    interrupt-parent = <&SOC_INTC>;
 
    [...]
 
    memory {
        /* When there is a calculation, please use "()" to include them */
        reg = <0x0 MEM_BASE 0x0 (3 * SIZE_GB)>;
        device_type = "memory";
    };
 
    cpus {
        #size-cells = <0>;
        #address-cells = <1>;
 
        /* Macros after "@" will be replaced */
        cpu0: cpu@CPU_HARDID {
            reg = <CPU_HARDID>;
            device_type = "cpu";
        };
    };
 
    /* Macros replace support phandle name, too */
    intc_a: intc-a {
        interrupt-controller;
    };
 
    intc_b: intc-b {
        interrupt-controller;
    };
 
    [...]
};

To generate the DTB:

import os, sys
 
RTT_ROOT = os.getenv('RTT_ROOT')
sys.path.append(RTT_ROOT + '/tools')
 
from building import *
import dtc
 
dtc.dts_to_dtb(RTT_ROOT, ["dummpy.dts"]

To append more include paths, for example, SoC DM headers:

[...]
 
dtc.dts_to_dtb(RTT_ROOT, ["dummpy.dts"], include_paths = ['dm/include', 'firmware'])

Multiple DTB

A single SoC may have different board variants. Example dummy.dtsi (common base):

/* SoC dummy */
/ {
    #address-cells = <2>;
    #size-cells = <2>;
    model = "Dummy SoC Board";
 
    [...]
 
    chosen {
        bootargs = "cma=8M coherent_pool=2M";
    };
 
    reserved-memory {
        #address-cells = <2>;
        #size-cells = <2>;
 
        isp_shm@100000 {
            reg = <0x0 0x100000 0x0 0x100000>;
        };
 
        dsp_shm@200000 {
            reg = <0x0 0x200000 0x0 0x100000>;
        };
    };
 
    dsp {
        status = "okay";
    };
 
    buddy {
        isp = <&{/reserved-memory/isp_shm@100000}>;
        dsp = <&{/reserved-memory/dsp_shm@200000}>;
    };
 
    uart0: uart {
        status = "disabled";
    };
 
    i2c0: i2c {
        status = "okay";
    };
 
    [...]
};

For a vendor-specific variant (Vendor A):

/* vendorA dummy */
#include "dummy.dtsi"
 
/ {
    /* No phandle name can modify in place */
    chosen {
        bootargs = "console=uart0 cma=8M coherent_pool=2M";
    };
};
 
/* Reference and modify direct if has phandle name */
&uart0 {
    status = "okay";
    pinctrl-0 = <&uart0_m1>;
};
 
&i2c0 {
    status = "disabled";
};

To remove nodes or properties (Vendor B):

/* vendorB dummy */
#include "dummy.dtsi"
 
/delete-node/ &dsp_shm;
 
/ {
    /* Delete in place if no phandle name */
    /delete-node/ dsp;
 
    /* Delete property */
    buddy {
        /delete-property/ dsp;
    };
};

To add new devices (Vendor C):

/* vendorC dummy */
#include "dummy.dtsi"
 
&i2c0 {
    rtc@0 {
        clock-frequency = <32768>;
    };
};

Build all DTBs together:

[...]
 
dtc.dts_to_dtb(RTT_ROOT, ["dummpy-vendorA.dts", "dummpy-vendorB.dts", "dummpy-vendorC.dts"])

This will produce dummpy-vendorA.dtb, dummpy-vendorB.dtb, and dummpy-vendorC.dtb

Warnings

DTC may produce warnings that are irrelevant or noisy. To suppress specific warnings:

[...]
 
dtc.dts_to_dtb(RTT_ROOT, ["dummpy.dts"], ignore_warning = ["simple_bus_reg", "unit_address_vs_reg", "clocks_is_cell", "gpios_property"])

Make sure your DTS is valid!

Raw options

DTC provides additional command-line options (see dtc –help). You can pass raw options like this:

[...]
 
dtc.dtb_to_dts(RTT_ROOT, "dummpy.dtb", options = "--quiet")
dtc.dts_to_dtb(RTT_ROOT, ["dummpy.dts"], options = "--quiet")