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Linux DTS(Device Tree Source)设备树详解之三(高通MSM8953实例分析篇)
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在前两篇中我们了解了DTS的背景基础知识以及发挥作用的流程，这篇文章我们以高通的MSM8953平台为例来添加一个基础的i2c设备（包含一个gpio中断）。
首先我们在该i2c设备的驱动中找到了匹配设备与驱动程序的compatible
static const struct of_device_id iqs263_of_match[] = {
{ .compatible = "azopteq,iqs263", },
{ },
}
由此compatible可以找到dts中对应的设备
kernel\arch\arm64\boot\dts\qcom\msm8953-mtp.dts
iqs263@44 { //Capacitive Touch Controller Driver
compatible = "azopteq,iqs263";
reg = <0x44>;
pinctrl-names = "default";
pinctrl-0 = <&iqs263_irq_config>;
vdd-supply = <&pm8953_l5>;
vio-supply = <&pm8953_l5>;
interrupt-parent = <&tlmm>;
interrupts = <48 0x2>;
azopteq,irq-gpio =<&tlmm 48 0x2>;
};
};
其中compatible属性标识的名字是与驱动程序中名字相匹配的
其中reg属性及@符号后的十六进制数字标识了该设备iqs263的i2c地址为0x44
&i2c_8前的&表明此处仅仅是对i2c_8节点的补充，我们可以找到该节点定义的地方
kernel\arch\arm64\boot\dts\qcom\msm8953.dtsi
i2c_8: i2c@7af8000 { /* BLSP2 QUP4 */
compatible = "qcom,i2c-msm-v2";
#address-cells = <1>;
#size-cells = <0>;
reg-names = "qup_phys_addr";
reg = <0x7af8000 0x600>;
interrupt-names = "qup_irq";
interrupts = <0 302 0>;
qcom,clk-freq-out = <400000>;
qcom,clk-freq-in = <19200000>;
clock-names = "iface_clk", "core_clk";
clocks = <&clock_gcc clk_gcc_blsp2_ahb_clk>,
<&clock_gcc clk_gcc_blsp2_qup4_i2c_apps_clk>;
pinctrl-names = "i2c_active", "i2c_sleep";
pinctrl-0 = <&i2c_8_active>;
pinctrl-1 = <&i2c_8_sleep>;
qcom,noise-rjct-scl = <0>;
qcom,noise-rjct-sda = <0>;
qcom,master-id = <84>;
dmas = <&dma_blsp2 10 64 0x20000020 0x20>,
<&dma_blsp2 11 32 0x20000020 0x20>;
dma-names = "tx", "rx";
};
rpm_bus: qcom,rpm-smd {
compatible = "qcom,rpm-smd";
rpm-channel-name = "rpm_requests";
rpm-channel-type = <15>; /* SMD_APPS_RPM */
};
这当中的大部分属性都与平台相关了，可以看到定义了该i2c接口的时钟源、中断格式等。这部分一般由平台提供，作为驱动工程师了解即可。
i2c_8节点中的pinctrl-0指向了定义其io口的节点i2c_8_active和i2c_8_sleep，代码如下可见该i2c的IO口为Gpio98和Gpio99
kernel\arch\arm64\boot\dts\qcom\msm8953-pinctrl.dtsi
tlmm: pinctrl@1000000 {
i2c_8 {
i2c_8_active: i2c_8_active {
/* active state */
mux {
pins = "gpio98", "gpio99";
function = "blsp_i2c8";
};
config {
pins = "gpio98", "gpio99";
drive-strength = <2>;
bias-disable;
};
};
i2c_8_sleep: i2c_8_sleep {
/* suspended state */
mux {
pins = "gpio98", "gpio99";
function = "gpio";
};
config {
pins = "gpio98", "gpio99";
drive-strength = <2>;
bias-disable;
};
};
};
iqs263_irq_config: iqs263_irq_config {
mux {
pins = "gpio48";
function = "gpio";
};
config {
pins = "gpio48";
drive-strength = <2>;
bias-pull-up;
};
};
iqs263节点中的pinctrl-0 属性指向了表明其io口属性的节点为iqs263_irq_config，相关代码也在2.3.1指示的msm8953-pinctrl.dtsi文件中。
其中定义了iqs263的中断IO脚为Gpio48
iqs263节点中的vdd-supply，vio-supply属性指示了表明iqs263芯片供电的引脚的节点pm8953_l5，代码如下
kernel\arch\arm64\boot\dts\qcom\msm8953-regulator.dtsi
rpm-regulator-ldoa5 {
status = "okay";
pm8953_l5: regulator-l5 {
regulator-min-microvolt = <1800000>;
regulator-max-microvolt = <1800000>;
qcom,init-voltage = <1800000>;
status = "okay";
};
};
iqs263的interrupts = <48 0x2>属性表明中断号为48,2代表下降沿触发
