* PCF857x-compatible I/O expanders The PCF857x-compatible chips have "quasi-bidirectional" I/O lines that can be driven high by a pull-up current source or driven low to ground. This combines the direction and output level into a single bit per line, which can't be read back. We can't actually know at initialization time whether a line is configured (a) as output and driving the signal low/high, or (b) as input and reporting a low/high value, without knowing the last value written since the chip came out of reset (if any). The only reliable solution for setting up line direction is thus to do it explicitly. Required Properties: - compatible: should be one of the following. - "maxim,max7328": For the Maxim MAX7378 - "maxim,max7329": For the Maxim MAX7329 - "nxp,pca8574": For the NXP PCA8574 - "nxp,pca8575": For the NXP PCA8575 - "nxp,pca9670": For the NXP PCA9670 - "nxp,pca9671": For the NXP PCA9671 - "nxp,pca9672": For the NXP PCA9672 - "nxp,pca9673": For the NXP PCA9673 - "nxp,pca9674": For the NXP PCA9674 - "nxp,pca9675": For the NXP PCA9675 - "nxp,pcf8574": For the NXP PCF8574 - "nxp,pcf8574a": For the NXP PCF8574A - "nxp,pcf8575": For the NXP PCF8575 - "ti,tca9554": For the TI TCA9554 - reg: I2C slave address. - gpio-controller: Marks the device node as a gpio controller. - #gpio-cells: Should be 2. The first cell is the GPIO number and the second cell specifies GPIO flags, as defined in . Only the GPIO_ACTIVE_HIGH and GPIO_ACTIVE_LOW flags are supported. Optional Properties: - lines-initial-states: Bitmask that specifies the initial state of each line. When a bit is set to zero, the corresponding line will be initialized to the input (pulled-up) state. When the bit is set to one, the line will be initialized the low-level output state. If the property is not specified all lines will be initialized to the input state. The I/O expander can detect input state changes, and thus optionally act as an interrupt controller. When the expander interrupt line is connected all the following properties must be set. For more information please see the interrupt controller device tree bindings documentation available at Documentation/devicetree/bindings/interrupt-controller/interrupts.txt. - interrupt-controller: Identifies the node as an interrupt controller. - #interrupt-cells: Number of cells to encode an interrupt source, shall be 2. - interrupt-parent: phandle of the parent interrupt controller. - interrupts: Interrupt specifier for the controllers interrupt. Please refer to gpio.txt in this directory for details of the common GPIO bindings used by client devices. Example: PCF8575 I/O expander node pcf8575: gpio@20 { compatible = "nxp,pcf8575"; reg = <0x20>; interrupt-parent = <&irqpin2>; interrupts = <3 0>; gpio-controller; #gpio-cells = <2>; interrupt-controller; #interrupt-cells = <2>; };