一、设备树作用　　

　　设备树存在的目的是将soc的uart、i2c、spi等外设信息以设备树文件的形式独立出内核，系统启动时，内核会将设备树读入。

二、dts、dtsi、dtb、dtc关系

　　设备树有.dts和.dtsi两种文件形式，.dtsi是.dts的公共部分，被dts包含。dtc是dts的编译器，将dtsi和dts编译成dtb。最终内核是读取dtb文件将设备树度进内核。dtc工具在linux源码/scripts/dtc 目录下。

        

三、设备树结构

uart0是节点标签，serial是节点名称，12100000是uart0寄存器首地址，在dts中可以通过@uart0来访问这个节点

下面是hi3559av100-demb.dts的部分设备树

#include "hi3559av100.dtsi"

/ {　　　　　　　　　　　　　　　　　　　　　　　　 以“/”开头
model = "Hisilicon HI3559AV100 DEMO Board";　　　　model指定制造商的设备型号
compatible = "hisilicon,hi3559av100";　　　　　　　　  compatible指定了系统的名称

aliases {
serial0 = &uart0;
serial1 = &uart1;

i2c0 = &i2c_bus0;
i2c1 = &i2c_bus1;

spi0 = &spi_bus0;
spi1 = &spi_bus1;

gpio0 = &gpio_chip0;
gpio1 = &gpio_chip1;
};

chosen {
bootargs = "mem=512M console=ttyAMA0,115200 clk_ignore_unused root=/dev/mtdblock2 rootfstype=yaffs2 rw mtdparts=hinand:1M(boot),9M(kernel),32M(rootfs),1M(this_bootargs_string_is_reserved_for_bootargs_form_uboot!!!_it_must_be_longer_than_bootargs_form_uboot!!!_this_bootargs_string_is_reserved_for_bootargs_form_uboot!!!_it_must_be_longer_than_bootargs_form_uboot!!!_this_bootargs_string_is_reserved_for_bootargs_form_uboot!!!_it_must_be_longer_than_bootargs_form_uboot!!!_this_bootargs_string_is_reserved_for_bootargs_form_uboot!!!_it_must_be_longer_than_bootargs_form_uboot!!!_this_bootargs_string_is_reserved_for_bootargs_form_uboot!!!_it_must_be_longer_than_bootargs_form_uboot!!!)";

linux,initrd-start = <0x60000040>;
linux,initrd-end = <0x61000000>;
};

cpus {
#address-cells = <2>;
#size-cells = <0>;

cpu@0 {
compatible = "arm,cortex-a53";
device_type = "cpu";
reg = <0x0 0x0>;
enable-method = "psci";
clock-latency = <100000>; /* From legacy driver */
cpu-idle-states = <&CPU_POWERDOWN &CPU_STANDBY>;
};

cpu@1 {
compatible = "arm,cortex-a53";
device_type = "cpu";
reg = <0x0 0x1>;
enable-method = "psci";
clock-latency = <200000>; /* From legacy driver */
cpu-idle-states = <&CPU_POWERDOWN &CPU_STANDBY>;
};
cpu@2 {
compatible = "arm,cortex-a73";
device_type = "cpu";
reg = <0x0 0x100>;
enable-method = "psci";
cpu-idle-states = <&CPU_POWERDOWN &CPU_STANDBY>;
vcc-supply = <&a73_regulator>;
};
cpu@3 {
compatible = "arm,cortex-a73";
device_type = "cpu";
reg = <0x0 0x101>;
enable-method = "psci";
operating-points = <
792000 796000
1296000 888000
1608000 988000
>;
clocks = <&clock HI3559AV100_A73_MUX>,
<&clock HI3559AV100_FIXED_24M>,
<&clock HI3559AV100_APLL_CLK>,
<&clock HI3559AV100_FIXED_1000M>;
clock-names = "a73_mux","24m","apll","1000m";
clock-latency = <400000>; /* From legacy driver */
cpu-idle-states = <&CPU_POWERDOWN &CPU_STANDBY>;
vcc-supply = <&a73_regulator>;
};

};

memory {
device_type = "memory";
reg = <0x0 0x44000000 0x2 0x0>; /* system memory base */
};
};

&uart0 {　　　　　　"&"表示追加节点属性，在"hi3516dv200.dtsi"文件中已经有uart0节点的描述，这里追加一个"status"属性，如果dtsi中已经有status属性，将会替换，如果没有则追加。
status = "okay";
};

&uart1 {
status = "okay";
};

四、设备树在系统中的位置　

　　设备树会被内核解析到/sys/firmware/devicetree/base，以hi3559为例，改目录下的文件如下所示：