在2.6.x的程式碼裡面對於PIN腳複用都是在對應的晶片的broad code裡面進行配置的，直接呼叫相關的特有API去設定。如我使用的AT91 MSA9260裡面的at91_set_GPIO_periph（）用於設定一個PIN為GPIO的模式，at91_set_A_periph（） 用於設定一個PIN為A mode。而且每家chip廠商提供的風格和形式都不相同。在3.x之後的程式碼裡面kernel引入了pinctl的驅動，對這些進行了更好的設計：

PINCTRL (PIN CONTROL) subsystem

This document outlines the pin control subsystem in Linux

This subsystem deals with:

- Enumerating and naming controllable pins

- Multiplexing of pins, pads, fingers (etc) see below for details

- Configuration of pins, pads, fingers (etc), such as software-controlled

  biasing and driving mode specific pins, such as pull-up/down, open drain,

  load capacitance etc. 

gpio0 {
pinctrl_gpio0: gpio0-0 {
atmel,pins =
<AT91_PIOB 16 AT91_PERIPH_B GPIO_ACTIVE_LOW/* CAN reset active Low */
AT91_PIOB 17 AT91_PERIPH_B GPIO_ACTIVE_HIGH>;/* CAN Power active High */
};

usart2: [email protected] {
/* ttyS3 -- RS485 */
/* DTR HW/SW enabled/disabled from userspace using ioctl */
linux,rs485-enabled-at-boot-time; /* enable RS485 mode in the bootup */
dtr-gpios = <&pioB 17 0>;  /*xxx, the AT91_PIN_PB17 is a dtr control signal. */
status = "okay";
};

gpio_is_valid(int number);

/* set as input or output, returning 0 or negative errno */
int gpio_direction_input(unsigned gpio);
int gpio_direction_output(unsigned gpio, int value);

/* GPIO INPUT:  return zero or nonzero */
int gpio_get_value(unsigned gpio);

/* GPIO OUTPUT */
void gpio_set_value(unsigned gpio, int value);