Sysfs interface for GPIO controller
On successful gpiochip_add(), a directory entry with a path such as /sys/class/gpio/gpiochipX/ will be created, where X is the GPIO controller base (the controller providing GPIOs starting at #X), with the following attributes:
base, whose value is the same asX, and which corresponds togpio_chip.base(if assigned statically) and is the first GPIO managed by this chip.label, which is provided for diagnostics (not always unique).ngpio, which tells how many GPIOs this controller provides (N to N + ngpio - 1). This is the same as defined ingpio_chip.ngpios.
All of the preceding attributes are read-only.
