u-boot/doc/device-tree-bindings/i2c/i2c.txt

U-Boot I2C
----------

U-Boot's I2C model has the concept of an offset within a chip (I2C target
device). The offset can be up to 4 bytes long, but is normally 1 byte,
meaning that offsets from 0 to 255 are supported by the chip. This often
corresponds to register numbers.

Apart from the controller-specific I2C bindings, U-Boot supports a special
property which allows the chip offset length to be selected.

Optional properties:
- u-boot,i2c-offset-len - length of chip offset in bytes. If omitted the
    default value of 1 is used.
- u-boot,i2c-transaction-bytes - the length of single I2C transaction on
    the bus. Some devices require more than single byte transmission
    (e.g. mc34708 mfd). This information is necessary to correctly
     initialize (put into idle state) I2C bus after soft reset.
- gpios = <sda ...>, <scl ...>;
  pinctrl-names = "default", "gpio";
  pinctrl-0 = <&i2c_xfer>;
  pinctrl-1 = <&i2c_gpio>;
    Pin description for I2C bus software deblocking.


Example
-------

i2c4: i2c@12ca0000 {
	cros-ec@1e {
		reg = <0x1e>;
		compatible = "google,cros-ec";
		i2c-max-frequency = <100000>;
		u-boot,i2c-offset-len = <0>;
		u-boot,i2c-transaction-bytes = <3>;
		ec-interrupt = <&gpx1 6 GPIO_ACTIVE_LOW>;
	};
};

&i2c1 {
	pinctrl-names = "default", "gpio";
	pinctrl-0 = <&i2c1_xfer>;
	pinctrl-1 = <&i2c1_gpio>;
	gpios = <&gpio1 26 GPIO_ACTIVE_LOW>, /* SDA */
		<&gpio1 27 GPIO_ACTIVE_LOW>; /* SCL */
};