20 设备树里声明i2c设备

参考内核源码目录里的Documentation/i2c/instantiating-devices
文档里主要的内容:

Method 1b: Declare the I2C devices via devicetree-------------------------------------------------This method has the same implications as method 1a. The declaration of I2Cdevices is here done via devicetree as subnodes of the master controller.Example:    i2c1: i2c@400a0000 {        /* ... master properties skipped ... */        clock-frequency = <100000>;           flash@50 {            compatible = "atmel,24c256";            reg = <0x50>;        };        pca9532: gpio@60 {            compatible = "nxp,pca9532";            gpio-controller;            #gpio-cells = <2>;            reg = <0x60>;        };    };

通过文档里的内容， 可以得知: i2c设备节点需要作为i2c控制器节点的子节点.
i2c设备节点的compatible属性值除了用于与设备驱动匹配以外，还作为设备名.
reg属性值为设备地址.也可以在设备节点里加入额外的属性.

---

如dht12接在第0个i2c控制器上，则修改内核源码目录arch/arm64/boot/dts/allwinner/sunxi-h3-h5.dts:

        i2c0: i2c@01c2ac00 {  /* 控制器的设备节点 */            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>;            mydht12 {   /* 增加的设备子节点  */                compatible = "mydht12";                reg = <0x5c>; /* 设备地址 */        /*  额外增加的属性，供i2c设备驱动使用  */                led-gpios = <&pio 0 17 GPIO_ACTIVE_HIGH>;             };        };

重编设备树并更新，重启系统后:

^_^ / # ls /sys/bus/i2c/devices/0-005c/  0-0068/  i2c-0/   i2c-1/   i2c-2/^_^ / # cat /sys/bus/i2c/devices/0-005c/name mydht12