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145 lines
4.0 KiB
Plaintext
145 lines
4.0 KiB
Plaintext
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* PiFace Digital, Device Tree Overlay.
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* Copyright (C) 2020 Thomas Preston <thomas.preston@codethink.co.uk>
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*
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* The PiFace Digital is a convenient breakout board for the Microchip mcp23s17
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* SPI GPIO port expander.
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*
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* The first eight GPIOs 0..7 (bank A) are connected to eight output terminals
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* and LEDs, plus two relays on the first two outputs. These output loads are
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* active-high.
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*
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* The next eight GPIOs 8..15 (bank B) are connected to eight input terminals
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* with four on-board switches connecting them to ground. Inputs devices are
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* therefore expected to bridge terminals to ground, so the mcp23s17 pullups are
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* activated for GPIO bank B.
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*
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* On PiFace Digital, the mcp23s17 is connected to the Raspberry Pi's SPI0 CS0
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* bus. Each SPI bus supports up to eight addressable child devices. The PiFace
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* Digital only supports addresses 0-4, which can be configured by jumpers JP1
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* and JP2.
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*
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* You can tell the driver about these jumper configurations with the
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* spi-present-mask bitmask:
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*
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* | JP1 | JP2 | dtoverlay line in /boot/config.txt |
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* | --- | --- | ------------------------------------------ |
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* | 0 | 0 | dtoverlay=pifacedigital |
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* | 0 | 0 | dtoverlay=pifacedigital:spi-present-mask=1 |
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* | 0 | 1 | dtoverlay=pifacedigital:spi-present-mask=2 |
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* | 1 | 0 | dtoverlay=pifacedigital:spi-present-mask=4 |
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* | 1 | 1 | dtoverlay=pifacedigital:spi-present-mask=8 |
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*
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* # Example
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* Set the dtoverlay config in /boot/config.txt and power off the Raspberry Pi:
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*
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* $ grep pifacedigital /boot/config.txt
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* dtoverlay=pifacedigital
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* $ sudo systemctl poweroff
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*
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* Attach the PiFace Digital and power on the Raspberry Pi.
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* Then use the libgpiod tools to query the device:
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*
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* $ sudo apt install gpiod
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* $ gpiodetect | grep mcp23s17
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* gpiochip2 [mcp23s17.0] (16 lines)
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*
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* Set GPIO outputs 0, 2 and 5:
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*
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* $ gpioset gpiochip2 0=1 2=1 5=1
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*
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* Get GPIO status (input GPIO 8..15 are high, because they are active-low):
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*
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* $ gpioget gpiochip2 {8..15}
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* 1 1 1 1 1 1 1 1
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*
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* And even monitor interrupts:
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*
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* $ gpiomon gpiochip2 {8..15}
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* event: FALLING EDGE offset: 11 timestamp: [1597361662.926741667]
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* event: RISING EDGE offset: 11 timestamp: [1597361663.062555051]
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*
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*/
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/dts-v1/;
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/plugin/;
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/ {
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compatible = "brcm,bcm2835";
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/* Disable exposing /dev/spidev0.0 */
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fragment@0 {
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target = <&spidev0>;
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__overlay__ {
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status = "disabled";
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};
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};
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/* Add the PiFace Digital device node to the spi0.0 device. */
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fragment@1 {
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target = <&spi0>;
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__overlay__ {
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status = "okay";
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#address-cells = <1>;
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#size-cells = <0>;
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pfdigital: pifacedigital@0 {
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compatible = "microchip,mcp23s17";
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reg = <0>;
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/* Set devices present with 8-bit mask. */
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microchip,spi-present-mask = <0x01>;
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spi-max-frequency = <500000>;
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gpio-controller;
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#gpio-cells = <2>;
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/* This device can pass through interrupts. */
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interrupt-controller;
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#interrupt-cells = <2>;
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/* INTB is connected to GPIO 25.
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* 0x8 active-low level-sensitive
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*/
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interrupts = <25 0x8>;
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interrupt-parent = <&gpio>;
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/* Configure pull-ups on bank B GPIOs */
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pinctrl-0 = <&pfdigital_irq &pfdigital_pullups>;
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pinctrl-names = "default";
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pfdigital_pullups: pinmux {
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pins =
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"gpio8",
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"gpio9",
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"gpio10",
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"gpio11",
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"gpio12",
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"gpio13",
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"gpio14",
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"gpio15";
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bias-pull-up;
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};
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};
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};
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};
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/* PiFace Digital mcp23s17 INTB pin is connected to GPIO 25. The INTB
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* pin is configured active-low (0 on interrupt), so expect to see
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* FALLING_EDGE when inputs are bridged to ground (switch is pressed).
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*/
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fragment@3 {
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target = <&gpio>;
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__overlay__ {
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pfdigital_irq: pifacedigital_irq {
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brcm,pins = <25>;
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brcm,function = <0>; /* input */
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};
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};
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};
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__overrides__ {
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spi-present-mask = <&pfdigital>, "microchip,spi-present-mask:0";
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};
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};
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