The Digi I/O Expander provides up to 39 GPIOs that can be used to control external peripherals and read digital signals.
Kernel configuration
You can manage the I/O Expander GPIO driver support through the following kernel configuration option:
-
Digi IO Expander (CONFIG_MFD_MCA_IOEXP)
Kernel driver
The I/O Expander GPIO driver is located at:
| File | Description |
|---|---|
Common codebase for GPIO driver (shared with MCA GPIOs) |
|
I/O Expander GPIO driver |
Device tree bindings and customization
The MCA GPIO device tree binding is documented at Documentation/devicetree/bindings/gpio/gpio-mca-ioexp.txt.
The GPIO controller inside the I/O Expander
mca_ioexp: mca_io@6e {
...
mca_ioexp_gpio: gpio {
compatible = "digi,mca-ioexp-gpio";
gpio-controller;
#gpio-cells = <2>;
};
};Using the I/O Expander GPIOs
The I/O Expander GPIO driver works as any other GPIO driver of the kernel. Its GPIOs can be accessed from the sysfs. See Documentation/gpio/sysfs.txt for more information.
Determine the GPIO controller
The system creates a sysfs entry for the I/O Expander GPIO controller and assigns it a GPIO base number.
You can tell the I/O Expander GPIO controller by reading the label of the different controller entries in /sys/class/gpio/.
~# ls /sys/class/gpio/ export gpiochip0 gpiochip128 gpiochip32 gpiochip456 gpiochip504 gpiochip64 gpiochip96 unexport ~# cat /sys/class/gpio/gpiochip465/label mca-gpio
In this example, the I/O Expander GPIO controller is /sys/class/gpio/gpiochip465.
Determine the number of GPIOs of the I/O Expander
To determine the number of GPIO pins of the controller:
~# cat /sys/class/gpio/gpiochip465/ngpio 39
In this example, the I/O Expander GPIO controller manages 39 GPIOs.
Identify I/O Expander GPIO indexes
The number of the gpiochip controller shows Linux base number for the I/O Expander GPIOs (465 in the example). You can also tell the base number with:
~# cat /sys/class/gpio/gpiochip465/base 465
This means that IOEXP_IO0 pin corresponds in Linux to GPIO index 465, IOEXP_IO1 corresponds to 466, and so on.
Some of the I/O Expander GPIO pins can be configured as ADC channels. When configured as ADC channel, a GPIO cannot be requested through the sysfs to be used as a standard GPIO.
For information about configuring an I/O Expander pin as ADC channel, see Analog-to-Digital Converter (ADC).
