linux字符设备驱动开发之设备树(1)
本文章参考正点原子相关教程,仅学习使用
为什么使用设备树?
linux内核3.x以前,采用板级信息描述设备,由于芯片发展速度快,造成linux内的板级信息太多,使系统太臃肿.所以采用设备树来简化表达.
文件目录: 内核源码位置/arch/arm/boot/dts
2.文件后缀
设备树文件扩展名(.dts),一个soc可以定制出很多板子,板子的通用信息通过后缀(.dtsi)文件描述.
一般地,(.dts)描述板级信息(开发板有那些设备),(.dtsi)表示SOC级信息(几个CPU,主频等等).
dtb:dts编译后的二进制文件.
dtc:编译工具
编译dts文件---->cd linux源目录 ----> make dtbs
3. DTS语法
小型设备树
dtsi: soc内部外部信息,cpu架构,主频,外设寄存器等等.
/ {
aliases {
can0 = &flexcan1;
...
};
cpus {
#address-cells = <1>;
#size-cells = <0>;
cpu0: cpu@0 {
compatible = "arm,cortex-a7";
device_type = "cpu";
reg = <0>;
clock-latency = <61036>; /* two CLK32 periods */
...
};
};
intc: interrupt-controller@00a01000 {
compatible = "arm,cortex-a7-gic";
#interrupt-cells = <3>;
interrupt-controller;
reg = <0x00a01000 0x1000>,
<0x00a02000 0x100>;
};
clocks {
#address-cells = <1>;
#size-cells = <0>;
ckil: clock@0 {
compatible = "fixed-clock";
reg = <0>;
#clock-cells = <0>;
clock-frequency = <32768>;
clock-output-names = "ckil";
};
...
};
soc {
#address-cells = <1>;
#size-cells = <1>;
compatible = "simple-bus";
interrupt-parent = <&gpc>;
ranges;
busfreq {
compatible = "fsl,imx_busfreq";
clocks = <&clks IMX6UL_CLK_PLL2_PFD2>, <&clks IMX6UL_CLK_PLL2_198M>,
...
};
gpmi: gpmi-nand@01806000{
compatible = "fsl,imx6ull-gpmi-nand", "fsl, imx6ul-gpmi-nand";
#address-cells = <1>;
#size-cells = <1>;
reg = <0x01806000 0x2000>, <0x01808000 0x4000>;
reg-names = "gpmi-nand", "bch";
interrupts = <GIC_SPI 15 IRQ_TYPE_LEVEL_HIGH>;
interrupt-names = "bch";
clocks = <&clks IMX6UL_CLK_GPMI_IO>,
<&clks IMX6UL_CLK_GPMI_APB>,
<&clks IMX6UL_CLK_GPMI_BCH>,
<&clks IMX6UL_CLK_GPMI_BCH_APB>,
<&clks IMX6UL_CLK_PER_BCH>;
clock-names = "gpmi_io", "gpmi_apb", "gpmi_bch",
"gpmi_bch_apb", "per1_bch";
dmas = <&dma_apbh 0>;
dma-names = "rx-tx";
status = "disabled";
};
.....
}
| 语法 | 解释 |
|---|---|
| / { } | 根节点 |
| aliases | 别名,定义别名方便访问节点 |
| nodename@unit addr | 节点名@外设基地址 |
| cpu0: cpu@0 | 标签与节点名用:隔开 |
| compatible | 兼容属性, 查找linux是否存在该兼容驱动 |
| model | 描述设备模块信息 |
| status | 设备状态信息 |
| address-cells | 决定子节点reg属性地址属性所占的字长(32) |
| size-cells | 决定子节点reg属性长度属性所占的字长(32) |
| reg | |
| range | 地址映射转换表,可以为空,也可以按照 |
| name | 记录节点名字,新版本已抛弃使用,老版本中存在 |
根节点的compatible
// /linux内核源码位置/arch/arm/boot/dts/imx6ull-9x9-evk.dts
/ {
model = "Freescale i.MX6 ULL 9x9 EVK Board";
compatible = "fsl,imx6ull-9x9-evk", "fsl,imx6ull";
....
}
// fsl,imx6ull-9x9-evk:使用的硬件设备
// fsl,imx6ull:设备使用的SOC
//系统检测是否支持该设备,支持则启动linux内核.
向节点添加,修改内容
通常不能在dtsi文件内添加子节点信息,这个导致所有板都必须支持该子节点.一般地,在特定板(dts)文件内添加子节点.
// imx6ull.dtsi
/{
...
i2c1: i2c@021a0000 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "fsl,imx6ul-i2c", "fsl,imx21-i2c";
reg = <0x021a0000 0x4000>;
interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clks IMX6UL_CLK_I2C1>;
status = "disabled";
};
...
};
// imx6ull-14x14-evk.dts
&i2c1 {
clock-frequency = <100000>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_i2c1>;
status = "okay";
// 子节点
mag3110@0e {
compatible = "fsl,mag3110";
reg = <0x0e>;
position = <2>;
};
// 子节点
ap3216c@1e {
compatible = "ap3216c";
reg = <0x1e>;
};
};