设备树规范学习

1、设备树概述：

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)>;};};
};

2、设备树的约定：

a、节点名称：

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。

b、路径名：

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。

c、属性：

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。

i、属性名：

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

ii、属性值：

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’