Linux Device Drivers Development

Claiming and configuring the GPIO

You can allocate and take ownership of a GPIO using the gpio_request() function:

static int  gpio_request(unsigned gpio, const char *label) 

gpio represents the GPIO number we are interested in, and label is the label used by the kernel for the GPIO in sysfs, as we can see in /sys/kernel/debug/gpio. You have to check the value returned, where 0 mean success and a negative error code is produced on an error. Once you've done this with the GPIO, it should be set free with the gpio_free() function:

void gpio_free(unsigned int gpio) 

If in doubt, you can use the gpio_is_valid() function to check whether this GPIO number is valid on the system prior to allocating it:

static bool gpio_is_valid(int number) 

Once ...