linux/Documentation/devicetree/bindings/i2c/i2c-mux-gpio.txt
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   1GPIO-based I2C Bus Mux
   2
   3This binding describes an I2C bus multiplexer that uses GPIOs to
   4route the I2C signals.
   5
   6                                  +-----+  +-----+
   7                                  | dev |  | dev |
   8    +------------+                +-----+  +-----+
   9    | SoC        |                   |        |
  10    |            |          /--------+--------+
  11    |   +------+ |  +------+    child bus A, on GPIO value set to 0
  12    |   | I2C  |-|--| Mux  |
  13    |   +------+ |  +--+---+    child bus B, on GPIO value set to 1
  14    |            |     |    \----------+--------+--------+
  15    |   +------+ |     |               |        |        |
  16    |   | GPIO |-|-----+            +-----+  +-----+  +-----+
  17    |   +------+ |                  | dev |  | dev |  | dev |
  18    +------------+                  +-----+  +-----+  +-----+
  19
  20Required properties:
  21- compatible: i2c-mux-gpio
  22- i2c-parent: The phandle of the I2C bus that this multiplexer's master-side
  23  port is connected to.
  24- mux-gpios: list of gpios used to control the muxer
  25* Standard I2C mux properties. See mux.txt in this directory.
  26* I2C child bus nodes. See mux.txt in this directory.
  27
  28Optional properties:
  29- idle-state: value to set the muxer to when idle. When no value is
  30  given, it defaults to the last value used.
  31
  32For each i2c child node, an I2C child bus will be created. They will
  33be numbered based on their order in the device tree.
  34
  35Whenever an access is made to a device on a child bus, the value set
  36in the revelant node's reg property will be output using the list of
  37GPIOs, the first in the list holding the least-significant value.
  38
  39If an idle state is defined, using the idle-state (optional) property,
  40whenever an access is not being made to a device on a child bus, the
  41GPIOs will be set according to the idle value.
  42
  43If an idle state is not defined, the most recently used value will be
  44left programmed into hardware whenever no access is being made to a
  45device on a child bus.
  46
  47Example:
  48        i2cmux {
  49                compatible = "i2c-mux-gpio";
  50                #address-cells = <1>;
  51                #size-cells = <0>;
  52                mux-gpios = <&gpio1 22 0 &gpio1 23 0>;
  53                i2c-parent = <&i2c1>;
  54
  55                i2c@1 {
  56                        reg = <1>;
  57                        #address-cells = <1>;
  58                        #size-cells = <0>;
  59
  60                        ssd1307: oled@3c {
  61                                compatible = "solomon,ssd1307fb-i2c";
  62                                reg = <0x3c>;
  63                                pwms = <&pwm 4 3000>;
  64                                reset-gpios = <&gpio2 7 1>;
  65                                reset-active-low;
  66                        };
  67                };
  68
  69                i2c@3 {
  70                        reg = <3>;
  71                        #address-cells = <1>;
  72                        #size-cells = <0>;
  73
  74                        pca9555: pca9555@20 {
  75                                compatible = "nxp,pca9555";
  76                                gpio-controller;
  77                                #gpio-cells = <2>;
  78                                reg = <0x20>;
  79                        };
  80                };
  81        };
  82