Linux Device Drivers Development

The GPIO interface and the device tree

Whatever interface you need to use GPIO for, how to specify GPIOs depends on the controller providing them, especially regarding its #gpio-cells property, which determines the number of cells used for a GPIO specifier. A GPIO specifier contains at least the controller phandle and one or more arguments, where the number of arguments on the #gpio-cells property of the controller that provides the GPIO. The first cell is generally the GPIO offset number on the controller, and the second represents the GPIO flags. GPIO properties should be named [<name>-]gpios], with <name> being the purpose of this GPIO for the device. Keep in mind this rule is a must for descriptor-based interfaces, and becomes <name>-gpios ...