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今天遇到了个I2C不通的问题，用的是I2C_8

msm8953.dtsi

i2c8 = &i2c_8;

i2c_8: i2c@7af8000 { /* BLSP2 QUP3 */
          compatible = "qcom,i2c-msm-v2";
           ...
           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_blsp1 10 64 0x20000020 0x20>,
                   <&dma_blsp1 11 32 0x20000020 0x20>;
           dma-names = "tx", "rx";
           status = "disabled";
   };

msm8953-pinctrl.dtsi

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;
                       };
               };
               ...
       }; 

该屏蔽的也都屏蔽了，可还是不通。于是去硬件测了测，发现根本没有波形。

正常的话CPU会通过I2C发出一段寻址的时序来寻找挂载在这个I2C上的IC，可是这个I2C什么波形都没有，我都开始怀疑人生了。

硬件告诉我这个I2C是需要供电才能正常工作的，可能是没有供电。

于是我把这路供电设置成

regulator-always-on

rpm-regulator-ldoa6 {
                 status = "okay";
                 pm8953_l6: regulator-l6 {
                         regulator-min-microvolt = <1800000>;
                         regulator-max-microvolt = <1800000>;
                         qcom,init-voltage = <1800000>;
                         regulator-always-on;
                         status = "okay";
                }
}

I2C就通了，问题解决。