GPIO kernel driver for Raspberry Pi.

Check the Wiki pages for details about

• Raspberry Pi Hardware
• Device Tree
• Software Implementation

 
Userspace access to GPIO Device Driver can be obrained via char device file or sysfs entries.

When module is loaded, /dev/test_gpio-20200000 character device is automatically created:

# insmod test_gpio.ko 
# ls -la /dev/test_gpio-20200000 
crw-------    1 root     root       10,  57 Jan  1 02:03 /dev/test_gpio-20200000

 
Module can optionally take an argument.
The "gpio" argument is an array of integers which represents GPIO pins for which sysfs entries will be created.

e.g.:
# insmod test_gpio.ko gpio="17,26"

# ls -la /sys/devices/platform/soc/20200000.test_gpio/testgpio*
-rw-r--r--    1 root     root          4096 Jan  1 00:05 /sys/devices/platform/soc/20200000.test_gpio/testgpio17
-rw-r--r--    1 root     root          4096 Jan  1 00:05 /sys/devices/platform/soc/20200000.test_gpio/testgpio26

 

Direction of GPIO pin can be input or output.
output GPIO pin can be set to high or low state.
GPIO pin can be set to generate interrupt on rising or falling edge.

 

Access via device file

To set pin as output, write pin number and high or low value to the device file:

# echo "17 high" > /dev/test_gpio-20200000
To set GPIO 17 to output low:
# echo "17 low" > /dev/test_gpio-20200000

To set pin as input, write pin number and in to the device file:
# echo "26 in" > /dev/test_gpio-20200000

To set interrupt for pin on rising egde, write pin number and rising to the device file:
# echo "26 rising" > /dev/test_gpio-20200000

To set interrupt for pin on falling egde, write pin number and falling to the device file:
# echo "26 falling" > /dev/test_gpio-20200000

To disable interrupt for pin , write pin number and none to the device file:
# echo "26 none" > /dev/test_gpio-20200000

Read from device file to get direction and value of all pins which direction is input or output:

# cat /dev/test_gpio-20200000 

  #   dir   value
  0. input    1
  1. input    1
  2. input    1

  ...
  ...

Access through sysfs

To set pin as output, write high or low value to the corresponding sysfs file:
# echo high > /sys/devices/platform/soc/20200000.test_gpio/testgpio17
# echo low > /sys/devices/platform/soc/20200000.test_gpio/testgpio17

To set pin as input, write in to the corresponding sysfs file:
# echo in > /sys/devices/platform/soc/20200000.test_gpio/testgpio26

To set interrupt for pin on rising egde, write rising to the corresponding sysfs file:
# echo rising > /sys/devices/platform/soc/20200000.test_gpio/testgpio26

To set interrupt for pin on falling egde, write falling to the corresponding sysfs file:
# echo falling > /sys/devices/platform/soc/20200000.test_gpio/testgpio26

To disable interrupt for pin , write none to the corresponding sysfs file:
# echo none > /sys/devices/platform/soc/20200000.test_gpio/testgpio26

To read value of some pin, read corresponding sysfs file:

# cat /sys/devices/platform/soc/20200000.test_gpio/testgpio26
input: 1