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Diffstat (limited to 'doc/device-tree-bindings/gpio/gpio-pcf857x.txt')
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1 files changed, 71 insertions, 0 deletions
diff --git a/doc/device-tree-bindings/gpio/gpio-pcf857x.txt b/doc/device-tree-bindings/gpio/gpio-pcf857x.txt new file mode 100644 index 0000000000..ada4e29733 --- /dev/null +++ b/doc/device-tree-bindings/gpio/gpio-pcf857x.txt @@ -0,0 +1,71 @@ +* 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 <dt-bindings/gpio/gpio.h>. 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>; + }; |