I am writing Linux user space application. where I want to invoke registered callback function in user space area from the kernel space.
i.e. interrupt arriving on GPIO pin(switch press event) and registered function getting called in user space.
is there any method is available to do this.
Thanks
I found below code after lot of digging and perfectly works for me.
Handling interrupts from GPIO In many cases, a GPIO input can be configured to generate an interrupt when it changes state, which allows you to wait for the interrupt rather than polling in an inefficient software loop. If the GPIO bit can generate interrupts, the file edge exists. Initially, it has the value none , meaning that it does not generate interrupts. To enable interrupts, you can set it to one of these values: • rising: Interrupt on rising edge • falling: Interrupt on falling edge • both: Interrupt on both rising and falling edges • none: No interrupts (default) You can wait for an interrupt using the poll() function with POLLPRI as the event. If you want to wait for a rising edge on GPIO 48, you first enable interrupts:
#echo 48 > /sys/class/gpio/export
#echo rising > /sys/class/gpio/gpio48/edge
Then, you use poll() to wait for the change, as shown in this code example:
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <poll.h>>
int main(void) {
int f;
struct pollfd poll_fds [1];
int ret;
char value[4];
int n;
f = open("/sys/class/gpio/gpio48", O_RDONLY);
if (f == -1) {
perror("Can't open gpio48");
return 1;
}
poll_fds[0].fd = f;
poll_fds[0].events = POLLPRI | POLLERR;
while (1) {
printf("Waiting\n");
ret = poll(poll_fds, 1, -1);
if (ret > 0) {
n = read(f, &value, sizeof(value));
printf("Button pressed: read %d bytes, value=%c\n", n, value[0]);
}
}
return 0;
}
Have to implement a handler in a kernel module that triggers e.g. a char device. From user space it could be accessed by polling (e.g. ioctl() calls). It seems that it is the only way at the moment.
