gpio pin is not exported in linux

Question

I have tried the following to export the gpio in linux userspace:

• In kernel config,

  Device Drivers --->
        --- GPIO Support
              [*] /sys/class/gpio/... (sysfs interface)
  

• GPIO=9

  echo $GPIO >/sys/class/gpio/export
  

• used gpio_export(9) in my code

• tried to export all the gpio. But no gpio is exported.

What am I missing in exporting gpio pins in sysfs..?

Answer 1

Have you requested for the GPIO via "gpio_request"? A call to gpio_export should export the GPIO to the sysfs for control.