tjh.dev
Linux kernel mirror (for testing)
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linux
1* PCF857x-compatible I/O expanders
2
3The PCF857x-compatible chips have "quasi-bidirectional" I/O lines that can be
4driven high by a pull-up current source or driven low to ground. This combines
5the direction and output level into a single bit per line, which can't be read
6back. We can't actually know at initialization time whether a line is configured
7(a) as output and driving the signal low/high, or (b) as input and reporting a
8low/high value, without knowing the last value written since the chip came out
9of reset (if any). The only reliable solution for setting up line direction is
10thus to do it explicitly.
11
12Required Properties:
13
14 - compatible: should be one of the following.
15 - "maxim,max7328": For the Maxim MAX7378
16 - "maxim,max7329": For the Maxim MAX7329
17 - "nxp,pca8574": For the NXP PCA8574
18 - "nxp,pca8575": For the NXP PCA8575
19 - "nxp,pca9670": For the NXP PCA9670
20 - "nxp,pca9671": For the NXP PCA9671
21 - "nxp,pca9672": For the NXP PCA9672
22 - "nxp,pca9673": For the NXP PCA9673
23 - "nxp,pca9674": For the NXP PCA9674
24 - "nxp,pca9675": For the NXP PCA9675
25 - "nxp,pcf8574": For the NXP PCF8574
26 - "nxp,pcf8574a": For the NXP PCF8574A
27 - "nxp,pcf8575": For the NXP PCF8575
28
29 - reg: I2C slave address.
30
31 - gpio-controller: Marks the device node as a gpio controller.
32 - #gpio-cells: Should be 2. The first cell is the GPIO number and the second
33 cell specifies GPIO flags, as defined in <dt-bindings/gpio/gpio.h>. Only the
34 GPIO_ACTIVE_HIGH and GPIO_ACTIVE_LOW flags are supported.
35
36Optional Properties:
37
38 - lines-initial-states: Bitmask that specifies the initial state of each
39 line. When a bit is set to zero, the corresponding line will be initialized to
40 the input (pulled-up) state. When the bit is set to one, the line will be
41 initialized the low-level output state. If the property is not specified
42 all lines will be initialized to the input state.
43
44 The I/O expander can detect input state changes, and thus optionally act as
45 an interrupt controller. When the expander interrupt line is connected all the
46 following properties must be set. For more information please see the
47 interrupt controller device tree bindings documentation available at
48 Documentation/devicetree/bindings/interrupt-controller/interrupts.txt.
49
50 - interrupt-controller: Identifies the node as an interrupt controller.
51 - #interrupt-cells: Number of cells to encode an interrupt source, shall be 2.
52 - interrupt-parent: phandle of the parent interrupt controller.
53 - interrupts: Interrupt specifier for the controllers interrupt.
54
55
56Please refer to gpio.txt in this directory for details of the common GPIO
57bindings used by client devices.
58
59Example: PCF8575 I/O expander node
60
61 pcf8575: gpio@20 {
62 compatible = "nxp,pcf8575";
63 reg = <0x20>;
64 interrupt-parent = <&irqpin2>;
65 interrupts = <3 0>;
66 gpio-controller;
67 #gpio-cells = <2>;
68 interrupt-controller;
69 #interrupt-cells = <2>;
70 };