DTSpec指定了一个称为设备树(device tree)的树状结构来描述系统的硬件信息。Bootloader将设备树文件加载到内存中，并将指向设备树文件地址的指针通过参数R2传递给kernel。
设备树是一个树形的数据结构，它的节点描述了系统中对应的设备。每个结点用属性-值（key-value）来描述设备的特征，除了root根节点以外，每个结点都有唯一的父节点。
以V3s为例：
#include <dt-bindings/interrupt-controller/arm-gic.h>
#include <dt-bindings/clock/sun8i-v3s-ccu.h>
#include <dt-bindings/reset/sun8i-v3s-ccu.h>
/ {
#address-cells = <1>;
#size-cells = <1>;
interrupt-parent = <&gic>;
chosen {
#address-cells = <1>;
#size-cells = <1>;
ranges;
simplefb_lcd: framebuffer@0 {
compatible = "allwinner,simple-framebuffer",
"simple-framebuffer";
allwinner,pipeline = "de0-lcd0";
clocks = <&ccu CLK_BUS_TCON0>, <&display_clocks 0>,
<&display_clocks 6>, <&ccu CLK_TCON0>;
status = "disabled";
};
};
cpus {
#address-cells = <1>;
#size-cells = <0>;
cpu@0 {
compatible = "arm,cortex-a7";
device_type = "cpu";
reg = <0>;
clocks = <&ccu CLK_CPU>;
};
};
de: display-engine {
compatible = "allwinner,sun8i-v3s-display-engine";
allwinner,pipelines = <&mixer0>;
status = "disabled";
};
timer {
compatible = "arm,armv7-timer";
interrupts = <GIC_PPI 13 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_LOW)>,
<GIC_PPI 14 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_LOW)>,
<GIC_PPI 11 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_LOW)>,
<GIC_PPI 10 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_LOW)>;
};
clocks {
#address-cells = <1>;
#size-cells = <1>;
ranges;
osc24M: osc24M_clk {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <24000000>;
clock-output-names = "osc24M";
};
osc32k: osc32k_clk {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <32768>;
clock-output-names = "osc32k";
};
};
soc {
compatible = "simple-bus";
#address-cells = <1>;
#size-cells = <1>;
ranges;
display_clocks: clock@1000000 {
compatible = "allwinner,sun8i-v3s-de2-clk";
reg = <0x01000000 0x100000>;
clocks = <&ccu CLK_DE>,
<&ccu CLK_BUS_DE>;
clock-names = "mod",
"bus";
resets = <&ccu RST_BUS_DE>;
#clock-cells = <1>;
#reset-cells = <1>;
};
mixer0: mixer@1100000 {
compatible = "allwinner,sun8i-v3s-de2-mixer";
reg = <0x01100000 0x100000>;
clocks = <&display_clocks 0>,
<&display_clocks 6>;
clock-names = "bus",
"mod";
resets = <&display_clocks 0>;
assigned-clocks = <&display_clocks 6>;
assigned-clock-rates = <150000000>;
ports {
#address-cells = <1>;
#size-cells = <0>;
mixer0_out: port@1 {
reg = <1>;
mixer0_out_tcon0: endpoint {
remote-endpoint = <&tcon0_in_mixer0>;
};
};
};
};
syscon: syscon@1c00000 {
compatible = "allwinner,sun8i-v3s-system-controller",
"syscon";
reg = <0x01c00000 0x1000>;
};
tcon0: lcd-controller@1c0c000 {
compatible = "allwinner,sun8i-v3s-tcon";
reg = <0x01c0c000 0x1000>;
interrupts = <GIC_SPI 86 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_TCON0>,
<&ccu CLK_TCON0>;
clock-names = "ahb",
"tcon-ch0";
clock-output-names = "tcon-pixel-clock";
#clock-cells = <0>;
resets = <&ccu RST_BUS_TCON0>;
reset-names = "lcd";
status = "disabled";
ports {
#address-cells = <1>;
#size-cells = <0>;
tcon0_in: port@0 {
reg = <0>;
tcon0_in_mixer0: endpoint {
remote-endpoint = <&mixer0_out_tcon0>;
};
};
tcon0_out: port@1 {
#address-cells = <1>;
#size-cells = <0>;
reg = <1>;
};
};
};
dma: dma-controller@01c02000 {
compatible = "allwinner,sun8i-v3s-dma";
reg = <0x01c02000 0x1000>;
interrupts = <GIC_SPI 50 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_DMA>;
resets = <&ccu RST_BUS_DMA>;
#dma-cells = <1>;
};
mmc0: mmc@1c0f000 {
compatible = "allwinner,sun7i-a20-mmc";
reg = <0x01c0f000 0x1000>;
clocks = <&ccu CLK_BUS_MMC0>,
<&ccu CLK_MMC0>,
<&ccu CLK_MMC0_OUTPUT>,
<&ccu CLK_MMC0_SAMPLE>;
clock-names = "ahb",
"mmc",
"output",
"sample";
resets = <&ccu RST_BUS_MMC0>;
reset-names = "ahb";
interrupts = <GIC_SPI 60 IRQ_TYPE_LEVEL_HIGH>;
pinctrl-names = "default";
pinctrl-0 = <&mmc0_pins>;
status = "disabled";
#address-cells = <1>;
#size-cells = <0>;
};
mmc1: mmc@1c10000 {
compatible = "allwinner,sun7i-a20-mmc";
reg = <0x01c10000 0x1000>;
clocks = <&ccu CLK_BUS_MMC1>,
<&ccu CLK_MMC1>,
<&ccu CLK_MMC1_OUTPUT>,
<&ccu CLK_MMC1_SAMPLE>;
clock-names = "ahb",
"mmc",
"output",
"sample";
resets = <&ccu RST_BUS_MMC1>;
reset-names = "ahb";
interrupts = <GIC_SPI 61 IRQ_TYPE_LEVEL_HIGH>;
pinctrl-names = "default";
pinctrl-0 = <&mmc1_pins>;
status = "disabled";
#address-cells = <1>;
#size-cells = <0>;
};
mmc2: mmc@1c11000 {
compatible = "allwinner,sun7i-a20-mmc";
reg = <0x01c11000 0x1000>;
clocks = <&ccu CLK_BUS_MMC2>,
<&ccu CLK_MMC2>,
<&ccu CLK_MMC2_OUTPUT>,
<&ccu CLK_MMC2_SAMPLE>;
clock-names = "ahb",
"mmc",
"output",
"sample";
resets = <&ccu RST_BUS_MMC2>;
reset-names = "ahb";
interrupts = <GIC_SPI 62 IRQ_TYPE_LEVEL_HIGH>;
status = "disabled";
#address-cells = <1>;
#size-cells = <0>;
};
usb_otg: usb@1c19000 {
compatible = "allwinner,sun8i-h3-musb";
reg = <0x01c19000 0x0400>;
clocks = <&ccu CLK_BUS_OTG>;
resets = <&ccu RST_BUS_OTG>;
interrupts = <GIC_SPI 71 IRQ_TYPE_LEVEL_HIGH>;
interrupt-names = "mc";
phys = <&usbphy 0>;
phy-names = "usb";
extcon = <&usbphy 0>;
status = "disabled";
};
usbphy: phy@1c19400 {
compatible = "allwinner,sun8i-v3s-usb-phy";
reg = <0x01c19400 0x2c>,
<0x01c1a800 0x4>;
reg-names = "phy_ctrl",
"pmu0";
clocks = <&ccu CLK_USB_PHY0>;
clock-names = "usb0_phy";
resets = <&ccu RST_USB_PHY0>;
reset-names = "usb0_reset";
status = "disabled";
#phy-cells = <1>;
};
ehci0: usb@01c1a000 {
compatible = "allwinner,sun8i-v3s-ehci", "generic-ehci";
reg = <0x01c1a000 0x100>;
interrupts = <GIC_SPI 72 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_EHCI0>, <&ccu CLK_BUS_OHCI0>;
resets = <&ccu RST_BUS_EHCI0>, <&ccu RST_BUS_OHCI0>;
status = "disabled";
};
ohci0: usb@01c1a400 {
compatible = "allwinner,sun8i-v3s-ohci", "generic-ohci";
reg = <0x01c1a400 0x100>;
interrupts = <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_EHCI0>, <&ccu CLK_BUS_OHCI0>,
<&ccu CLK_USB_OHCI0>;
resets = <&ccu RST_BUS_EHCI0>, <&ccu RST_BUS_OHCI0>;
status = "disabled";
};
ccu: clock@1c20000 {
compatible = "allwinner,sun8i-v3s-ccu";
reg = <0x01c20000 0x400>;
clocks = <&osc24M>, <&osc32k>;
clock-names = "hosc", "losc";
#clock-cells = <1>;
#reset-cells = <1>;
};
rtc: rtc@1c20400 {
compatible = "allwinner,sun6i-a31-rtc";
reg = <0x01c20400 0x54>;
interrupts = <GIC_SPI 40 IRQ_TYPE_LEVEL_HIGH>,
<GIC_SPI 41 IRQ_TYPE_LEVEL_HIGH>;
};
pio: pinctrl@1c20800 {
compatible = "allwinner,sun8i-v3s-pinctrl";
reg = <0x01c20800 0x400>;
interrupts = <GIC_SPI 15 IRQ_TYPE_LEVEL_HIGH>,
<GIC_SPI 17 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_PIO>, <&osc24M>, <&osc32k>;
clock-names = "apb", "hosc", "losc";
gpio-controller;
#gpio-cells = <3>;
interrupt-controller;
#interrupt-cells = <3>;
emac_rgmii_pins: emac-rgmii-pins {
pins = "PD0", "PD1", "PD2", "PD3", "PD4",
"PD5", "PD7", "PD8", "PD9", "PD10",
"PD12", "PD13", "PD15", "PD16", "PD17";
function = "emac";
drive-strength = <40>;
};
i2c0_pins: i2c0-pins {
pins = "PB6", "PB7";
function = "i2c0";
};
pwm0_pins: pwm0 {
pins = "PB4";
function = "pwm0";
};
uart0_pb_pins: uart0-pb-pins {
pins = "PB8", "PB9";
function = "uart0";
};
lcd_rgb666_pins_a: lcd-rgb666-pe {
pins = "PE0", "PE1", "PE2", "PE3", "PE4", "PE5",
"PE6", "PE7", "PE8", "PE9", "PE10", "PE11",
"PE12", "PE13", "PE14", "PE15", "PE16", "PE17",
"PE18", "PE19", "PE23", "PE24";
function = "lcd";
};
mmc0_pins: mmc0-pins {
pins = "PF0", "PF1", "PF2", "PF3",
"PF4", "PF5";
function = "mmc0";
drive-strength = <30>;
bias-pull-up;
};
mmc1_pins: mmc1-pins {
pins = "PG0", "PG1", "PG2", "PG3",
"PG4", "PG5";
function = "mmc1";
drive-strength = <30>;
bias-pull-up;
};
spi0_pins: spi0-pins {
pins = "PC0", "PC1", "PC2", "PC3";
function = "spi0";
};
};
timer@1c20c00 {
compatible = "allwinner,sun4i-a10-timer";
reg = <0x01c20c00 0xa0>;
interrupts = <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH>,
<GIC_SPI 19 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&osc24M>;
};
wdt0: watchdog@1c20ca0 {
compatible = "allwinner,sun6i-a31-wdt";
reg = <0x01c20ca0 0x20>;
interrupts = <GIC_SPI 25 IRQ_TYPE_LEVEL_HIGH>;
};
pwm: pwm@1c21400 {
compatible = "allwinner,sun8i-v3s-pwm",
"allwinner,sun7i-a20-pwm";
reg = <0x01c21400 0x400>;
clocks = <&osc24M>;
#pwm-cells = <3>;
status = "disabled";
};
lradc: lradc@1c22800 {
compatible = "allwinner,sun4i-a10-lradc-keys";
reg = <0x01c22800 0x400>;
interrupts = <GIC_SPI 30 IRQ_TYPE_LEVEL_HIGH>;
status = "disabled";
};
codec: codec@01c22c00 {
#sound-dai-cells = <0>;
compatible = "allwinner,sun8i-v3s-codec";
reg = <0x01c22c00 0x400>;
interrupts = <GIC_SPI 29 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_CODEC>, <&ccu CLK_AC_DIG>;
clock-names = "apb", "codec";
resets = <&ccu RST_BUS_CODEC>;
dmas = <&dma 15>, <&dma 15>;
dma-names = "rx", "tx";
allwinner,codec-analog-controls = <&codec_analog>;
status = "disabled";
};
codec_analog: codec-analog@01c23000 {
compatible = "allwinner,sun8i-v3s-codec-analog";
reg = <0x01c23000 0x4>;
};
uart0: serial@1c28000 {
compatible = "snps,dw-apb-uart";
reg = <0x01c28000 0x400>;
interrupts = <GIC_SPI 0 IRQ_TYPE_LEVEL_HIGH>;
reg-shift = <2>;
reg-io-width = <4>;
clocks = <&ccu CLK_BUS_UART0>;
resets = <&ccu RST_BUS_UART0>;
status = "disabled";
};
uart1: serial@1c28400 {
compatible = "snps,dw-apb-uart";
reg = <0x01c28400 0x400>;
interrupts = <GIC_SPI 1 IRQ_TYPE_LEVEL_HIGH>;
reg-shift = <2>;
reg-io-width = <4>;
clocks = <&ccu CLK_BUS_UART1>;
resets = <&ccu RST_BUS_UART1>;
status = "disabled";
};
uart2: serial@1c28800 {
compatible = "snps,dw-apb-uart";
reg = <0x01c28800 0x400>;
interrupts = <GIC_SPI 2 IRQ_TYPE_LEVEL_HIGH>;
reg-shift = <2>;
reg-io-width = <4>;
clocks = <&ccu CLK_BUS_UART2>;
resets = <&ccu RST_BUS_UART2>;
status = "disabled";
};
i2c0: i2c@1c2ac00 {
compatible = "allwinner,sun6i-a31-i2c";
reg = <0x01c2ac00 0x400>;
interrupts = <GIC_SPI 6 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_I2C0>;
resets = <&ccu RST_BUS_I2C0>;
pinctrl-names = "default";
pinctrl-0 = <&i2c0_pins>;
status = "disabled";
#address-cells = <1>;
#size-cells = <0>;
};
i2c1: i2c@1c2b000 {
compatible = "allwinner,sun6i-a31-i2c";
reg = <0x01c2b000 0x400>;
interrupts = <GIC_SPI 7 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_I2C1>;
resets = <&ccu RST_BUS_I2C1>;
status = "disabled";
#address-cells = <1>;
#size-cells = <0>;
};
emac: ethernet@1c30000 {
compatible = "allwinner,sun8i-h3-emac";
syscon = <&syscon>;
reg = <0x01c30000 0x10000>;
interrupts = <GIC_SPI 82 IRQ_TYPE_LEVEL_HIGH>;
interrupt-names = "macirq";
resets = <&ccu RST_BUS_EMAC>;
reset-names = "stmmaceth";
clocks = <&ccu CLK_BUS_EMAC>;
clock-names = "stmmaceth";
status = "disabled";
mdio: mdio {
#address-cells = <1>;
#size-cells = <0>;
compatible = "snps,dwmac-mdio";
};
mdio-mux {
compatible = "allwinner,sun8i-h3-mdio-mux";
#address-cells = <1>;
#size-cells = <0>;
mdio-parent-bus = <&mdio>;
/* Only one MDIO is usable at the time */
internal_mdio: mdio@1 {
compatible = "allwinner,sun8i-h3-mdio-internal";
reg = <1>;
#address-cells = <1>;
#size-cells = <0>;
int_mii_phy: ethernet-phy@1 {
compatible = "ethernet-phy-ieee802.3-c22";
reg = <1>;
clocks = <&ccu CLK_BUS_EPHY>;
resets = <&ccu RST_BUS_EPHY>;
};
};
external_mdio: mdio@2 {
reg = <2>;
#address-cells = <1>;
#size-cells = <0>;
};
};
};
spi0: spi@1c68000 {
compatible = "allwinner,sun8i-h3-spi";
reg = <0x01c68000 0x1000>;
interrupts = <GIC_SPI 65 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&ccu CLK_BUS_SPI0>, <&ccu CLK_SPI0>;
clock-names = "ahb", "mod";
pinctrl-names = "default";
pinctrl-0 = <&spi0_pins>;
resets = <&ccu RST_BUS_SPI0>;
status = "disabled";
#address-cells = <1>;
#size-cells = <0>;
};
gic: interrupt-controller@1c81000 {
compatible = "arm,gic-400";
reg = <0x01c81000 0x1000>,
<0x01c82000 0x1000>,
<0x01c84000 0x2000>,
<0x01c86000 0x2000>;
interrupt-controller;
#interrupt-cells = <3>;
interrupts = <GIC_PPI 9 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_HIGH)>;
};
};
};
设备树中的每个节点都应该遵循以下的约定：
node-name@unit-address
node-name指定节点的名称。它的长度应为1到31个字符，并且应该只包含表中所示的字符。
| 字符 | 描述 |
|---|---|
| 0-9 | 数字 |
| a-z | 小写字母 |
| A-Z | 大写字母 |
| , | 逗号 |
| . | 句号 |
| _ | 下划线 |
| + | 加号 |
| - | 短斜杠 |
节点名称应以小写或大写字符开头，并应描述设备的常规类型。名称中的单元地址组件特定于节点所在的总线类型。unit-address必须与节点的reg属性中指定的第一个地址匹配。如果节点没有reg属性，则必须省略@unit-address，并且节点名称将节点与树中同一级别的其他节点区分开来。特定总线的绑定可以为reg属性和unit-address的格式指定更多，更具体的要求。根节点没有节点名和unit-address。它由正斜杠/标识。
设备树中的一个结点能够被从根结点开始的绝对路径所唯一标识，能逐层查找到所描述的结点。制定一个设备路径的规则是：
/node-name-1/node-name-2/node-name-N
例如，访问CPU0的路径是：
/cpus/cpu@0
路径的根节点是/，如果根节点的绝对路径没问题，那么unit-address可以被省略。
设备树中的每个结点都有属性来描述结点的特性。属性由键值对名字和值组成。
由表中的字符组成：
| 字符 | 描述 |
|---|---|
| 0-9 | 数字 |
| a-z | 小写字符 |
| A-Z | 大写字符 |
| , | 逗号 |
| . | 句号 |
| _ | 下划线 |
| + | 加号 |
| ? | 问号 |
| # | #号 |
属性值是一个包含属性相关信息的数组。如果它表达的是true-false信息，那么它可能是一个空值。
表描述了 DTSpec 定义的一组基本值类型。
| 值 | 描述 |
|---|---|
| 值是empty。用来表示这个属性它自己是否存在的真假(true-false)信息。 | |
| big-endian格式的32位整数。例如32位值 0x11223344 在内存中的形式为: | |
| address 11 | |
| address+1 22 | |
| address+2 33 | |
| address+3 44 | |
| big-endian格式的64位整数，它由两个组成。例如0x1122334455667788将被表示为2个单元:<0x11223344 0x4455667788> 它在内存中的形式为： | |
| address 11 | |
| address+1 22 | |
| address+2 33 | |
| address+3 44 | |
| address+4 55 | |
| address+5 66 | |
| address+6 77 | |
| address+7 88 | |
| < string > | 字符串是可打印的字符(不能是空格等)。例如"hello"它在内存中的形式为： |
| address ‘h’ | |
| address+1 ‘e’ | |
| address+2 ‘l’ | |
| address+3 ‘l’ | |
| address+4 ‘o’ | |
| address+5 ‘\0’ | |
| < stringlist > | 由多个组成的字符串列表。如"hello",“world”,他在内存中的形式为： |
| address ‘h’ | |
| address+1 ‘e’ | |
| address+2 ‘l’ | |
| address+3 ‘l’ | |
| address+4 ‘o’ | |
| address+5 ‘\0’ | |
| address+6 ‘w’ | |
| address+7 ‘o’ | |
| address+8 ‘r’ | |
| address+9 ‘l’ | |
| address+10 ‘d’ | |
| address+11 ‘\0’ |