Device Tree

Device tree is for describe the peripheral HW. It not noly can describe the detectable devices, but also can be used for non-detectable devices

non-detectable device: Like memory information, flash information, UARTs, GPIOs …etc.

Device Tree Source (.dts)

root

/: This is root for device tree.

/ {
    
    name = "device-tree-example";
    model = "device model name";
    compatiable = "deive-tree";
    #address-cells = <2>;
    #size-cells = <2>;
    # linux,phandle = <0>;
}

node

[aliae_name:] node-name[@unit-address] {
    [properties definitions]
    [child nodes]
};

[]: means option

[aliae_name:] node-name[@unit-address] :
- unit-address: indicate the address mapping to device.
- if the node doesn't have "reg" property, the unit-address can't be exist.

properties definitions:

describe the node property

the property can be no assigned value. e.g properties = [value]

value :

can be a value or multiple value.

address = <1>;
address2 = [0x00001 0x20000];

can be string lists

device_type = "memory";
name = "PowerPC,970";

Property value

properties attirbute:
Standard Properties
Here are list some special properites.

address-cells and #size-cells :

The #address-cells and #size-cells properties may be used in any device node that has children in the devicetree hierarchy and describes how child device nodes should be addressed.

The #address-cells property defines the number of <u32> cells used to encode the address field in a child node’s reg property.

The #size-cells property defines the number of <u32> cells used to encode the size field in a child node’s reg property

    e.g: 
    #address-cells = <2>;
    #size-celss = <2>;
    memory@0 {
        device_type = "memory";
        reg = <0x000000000 0x00000000 0x00000000 0x80000000>;
    };

reg will use <address1, size1, address2, size2, …>

phandle:

A phandle value is a way to reference another node in the devicetree

In an array, the "&" reference will expand to a phandle.

mydevice: mydev {
    compatiable = "mydevice_list";
    pincontrol = <&my_pin_ctrl>;
}

maybe in another dtsi

my_pin_ctrl: my_pin_ctrl {
    ....
};

Outside an arry, the "&" reference will expand to the path of the node you're referring to.

label:node {
    #address-cell = <1>;
    #size-cells = <0>;
}

&label {
    ...;
};

This means

label:node {
    #address-cell = <1>;
    #size-cells = <0>;
    ....;
}

Device tree code trace and How to load into kernel

[TBD]

how to build

$ dtc -@ -I dts -O dtb -o <output>.dtbo <src>.dts

ref

Introduction to Linux kernel
driver programming
Device Tree（二）：基本概念
 Device Tree（三）：代码分析
 Device Tree（四）：文件结构解析
 example in linux kernel

dtsi example
dts example
Device Tree PIN defineitions
Device match to device driver

Device Tree

Device Tree Source (.dts)

root

node

Device tree code trace and How to load into kernel

how to build

ref

Read more

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