linux/linux-5.4.31/Documentation/devicetree/bindings/mux/mux-controller.txt

Common multiplexer controller bindings
======================================

A multiplexer (or mux) controller will have one, or several, consumer devices
that uses the mux controller. Thus, a mux controller can possibly control
several parallel multiplexers. Presumably there will be at least one
multiplexer needed by each consumer, but a single mux controller can of course
control several multiplexers for a single consumer.

A mux controller provides a number of states to its consumers, and the state
space is a simple zero-based enumeration. I.e. 0-1 for a 2-way multiplexer,
0-7 for an 8-way multiplexer, etc.


Consumers
---------

Mux controller consumers should specify a list of mux controllers that they
want to use with a property containing a 'mux-ctrl-list':

	mux-ctrl-list ::= <single-mux-ctrl> [mux-ctrl-list]
	single-mux-ctrl ::= <mux-ctrl-phandle> [mux-ctrl-specifier]
	mux-ctrl-phandle : phandle to mux controller node
	mux-ctrl-specifier : array of #mux-control-cells specifying the
			     given mux controller (controller specific)

Mux controller properties should be named "mux-controls". The exact meaning of
each mux controller property must be documented in the device tree binding for
each consumer. An optional property "mux-control-names" may contain a list of
strings to label each of the mux controllers listed in the "mux-controls"
property.

Drivers for devices that use more than a single mux controller can use the
"mux-control-names" property to map the name of the requested mux controller
to an index into the list given by the "mux-controls" property.

mux-ctrl-specifier typically encodes the chip-relative mux controller number.
If the mux controller chip only provides a single mux controller, the
mux-ctrl-specifier can typically be left out.

Example:

	/* One consumer of a 2-way mux controller (one GPIO-line) */
	mux: mux-controller {
		compatible = "gpio-mux";
		#mux-control-cells = <0>;

		mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>;
	};

	adc-mux {
		compatible = "io-channel-mux";
		io-channels = <&adc 0>;
		io-channel-names = "parent";

		mux-controls = <&mux>;
		mux-control-names = "adc";

		channels = "sync", "in";
	};

Note that in the example above, specifying the "mux-control-names" is redundant
because there is only one mux controller in the list. However, if the driver
for the consumer node in fact asks for a named mux controller, that name is of
course still required.

	/*
	 * Two consumers (one for an ADC line and one for an i2c bus) of
	 * parallel 4-way multiplexers controlled by the same two GPIO-lines.
	 */
	mux: mux-controller {
		compatible = "gpio-mux";
		#mux-control-cells = <0>;

		mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>,
			    <&pioA 1 GPIO_ACTIVE_HIGH>;
	};

	adc-mux {
		compatible = "io-channel-mux";
		io-channels = <&adc 0>;
		io-channel-names = "parent";

		mux-controls = <&mux>;

		channels = "sync-1", "in", "out", "sync-2";
	};

	i2c-mux {
		compatible = "i2c-mux";
		i2c-parent = <&i2c1>;

		mux-controls = <&mux>;

		#address-cells = <1>;
		#size-cells = <0>;

		i2c@0 {
			reg = <0>;
			#address-cells = <1>;
			#size-cells = <0>;

			ssd1307: oled@3c {
				/* ... */
			};
		};

		i2c@3 {
			reg = <3>;
			#address-cells = <1>;
			#size-cells = <0>;

			pca9555: pca9555@20 {
				/* ... */
			};
		};
	};


Mux controller nodes
--------------------

Mux controller nodes must specify the number of cells used for the
specifier using the '#mux-control-cells' property.

Optionally, mux controller nodes can also specify the state the mux should
have when it is idle. The idle-state property is used for this. If the
idle-state is not present, the mux controller is typically left as is when
it is idle. For multiplexer chips that expose several mux controllers, the
idle-state property is an array with one idle state for each mux controller.

The special value (-1) may be used to indicate that the mux should be left
as is when it is idle. This is the default, but can still be useful for
mux controller chips with more than one mux controller, particularly when
there is a need to "step past" a mux controller and set some other idle
state for a mux controller with a higher index.

Some mux controllers have the ability to disconnect the input/output of the
multiplexer. Using this disconnected high-impedance state as the idle state
is indicated with idle state (-2).

These constants are available in

      #include <dt-bindings/mux/mux.h>

as MUX_IDLE_AS_IS (-1) and MUX_IDLE_DISCONNECT (-2).

An example mux controller node look like this (the adg972a chip is a triple
4-way multiplexer):

	mux: mux-controller@50 {
		compatible = "adi,adg792a";
		reg = <0x50>;
		#mux-control-cells = <1>;

		idle-state = <MUX_IDLE_DISCONNECT MUX_IDLE_AS_IS 2>;
	};