Drivers for such devices should provide:
- Methods to establish GPIO direction (input and output).
- Methods used to access GPIO values (get and set).
- Methods to map a given GPIO to IRQ and return the associated number.
- Flag saying whether calls to its methods may sleep. This is very important.
- An optional debugfs dump method (showing extra state such as pullup config).
- An optional number called a base number, from which GPIO numbering should start. It will be automatically assigned if omitted.
In the kernel, a GPIO controller is represented as an instance of struct gpio_chip, defined in linux/gpio/driver.h:
struct gpio_chip {
const char *label;
struct device *dev;
struct module *owner;
int (*request)(struct gpio_chip *chip, unsigned offset);
void (*free)(struct gpio_chip *chip, unsigned offset);
int (*get_direction)(struct...