This section describes about the kernel configurations for GPIO driver
The default kernel configuration enables support for GPIO driver (built into the kernel).
To enable or disable GPIO driver from kernel build, follow these steps:
$ make CROSS_COMPILE=arm-none-linux-gnueabi- ARCH=arm menuconfig
- Select Device Drivers from the main menu.
Power management options --- > [*] Networking support --- > Device Drivers --- > File systems --- > ... ...
- Select GPIO Support from the menu.
PPS support --- > PTP clock support --- > -*- GPIO Support --- > < > Dallas's 1-wire support --- > ... ...
Sysfs entries configuration
GPIO can be access using SYSFS entries from User Space. For that Select /sys/class/gpio/... (sysfs interface) from the GPIO support.
[ ] Debug GPIO calls [*] /sys/class/gpio/... (sysfs interface) *** Memory mapped GPIO drivers: *** < > Basic memory-mapped GPIO controllers support ... ...
- After doing driver selection, exit and save the kernel configuration when prompted.
GPIO pin is also used as a interrupt source, these are the general usage of IRQ handling using GPIO lines.
- Map GPIO number to corresponding IRQ number, GPIO 0 need not use IRQ 0
irq_num = gpio_to_irq(30)
- Request IRQ, make sure that irq_num should be non-error value
request_irq(irq_num, handler, 0, "gpio_test", NULL);
- Set IRQ type Raising/Falling/Level triggered
- During the clean-up path free the IRQ and gpio
free_irq(irq_num, NULL); gpio_free(30);
- Allocate memory to GPIO line, can be achieved by doing
err = gpio_request(30, "sample_name");
- Depending on the requirement set GPIO as input or output pin then set gpio value as high or low.
Setting the GPIO pin 30 as input
Make pin 30 as output and set the value as high.
Exporting that particular pin (30) to sysfs entry then use this API
Get value from GPIO pin
User Space - Sysfs control
- Enable GPIO sysfs support in kernel configuration and build the kernel
Device Drivers --- > GPIO Support --- > /sys/class/gpio/... (sysfs interface)
- Sysfs entries
- Export the particular GPIO pin for user control. GPIO30 is taken as example.
$ echo 30 > /sys/class/gpio/export
- Change the GPIO pin direction to in/out
$ echo "out" > /sys/class/gpio/gpio30/direction
$ echo "in" > /sys/class/gpio/gpio30/direction
- Change the value
$ echo 1 > /sys/class/gpio/gpio30/value
$ echo 0 > /sys/class/gpio/gpio30/value
- Unexport the GPIO pin
$ echo 30 > /sys/class/gpio/unexport
Note: GPIO's which are used already in the drivers can not be control from sysfs, unless until driver export that particular pin.
Run these commands for knowing what are the GPIO's already requested in the drivers.
$ mount -t debugfs debugfs /sys/kernel/debug
$ cat /sys/kernel/debug/gpio