基于BarrierBreaker版本，基于AR9331 AP121 Demo单板 来进行描述
1.灯
A.在mach-ap121.c中，定义了灯所对应的GPIO定义：
#define AP121_GPIO_LED_WLAN 0
#define AP121_GPIO_LED_USB 1
并定义了灯的GPIO结构对象：
static struct gpio_led ap121_leds_gpio[] __initdata = {
{
.name = "ap121:green:usb",
.gpio = AP121_GPIO_LED_USB,
.active_low = 0,
},
{
.name = "ap121:green:wlan",
.gpio = AP121_GPIO_LED_WLAN,
.active_low = 0,
},
}
在初始化函数：ap121_setup 中，利用ath79_register_leds_gpio(-1, ARRAY_SIZE(ap121_leds_gpio), ap121_leds_gpio);实现了LED device的注册。此函数调用后，会创建platform类型的设备，并和leds-gpio驱动(leds-gpio.c)实现了绑定。这样，就会在/sys/devices/platform/leds-gpio/目录中，产生对应的led灯的控制目录：
drwxr-xr-x 2 root root 0 Jan 1 1970 ap121:green:usb
drwxr-xr-x 2 root root 0 Jan 1 1970 ap121:green:wlan
B.进入上述任意一个目录，如：ap121:green:wlan，会有如下文件：
-rw-r--r-- 1 root root 4096 Jan 15 06:19 brightness
lrwxrwxrwx 1 root root 0 Jan 15 06:04 device -> ../../../leds-gpio
-r--r--r-- 1 root root 4096 Jan 15 06:04 max_brightness
lrwxrwxrwx 1 root root 0 Jan 15 06:04 subsystem -> ../../../../../class/leds
-rw-r--r-- 1 root root 4096 Jan 15 06:04 trigger
-rw-r--r-- 1 root root 4096 Jan 15 06:04 uevent
则通过 echo 1 > brightness，就可以控制灯亮； echo 0 > brightness，就可以控制灯灭
2.按键
A.在mach-ap121.c中，定义了按键对应的GPIO以及数据结构对象：
#define AP121_GPIO_BTN_JUMPSTART 11
#define AP121_GPIO_BTN_RESET 12
以及
static struct gpio_keys_button ap121_gpio_keys[] __initdata = {
{
.desc = "jumpstart button",
.type = EV_KEY,
.code = KEY_WPS_BUTTON, //定义在gpio-button-hotplug.c
.debounce_interval = AP121_KEYS_DEBOUNCE_INTERVAL,
.gpio = AP121_GPIO_BTN_JUMPSTART,
.active_low = 1,
},
{
.desc = "reset button",
.type = EV_KEY,
.code = KEY_RESTART, //定义在gpio-button-hotplug.c
.debounce_interval = AP121_KEYS_DEBOUNCE_INTERVAL,
.gpio = AP121_GPIO_BTN_RESET,
.active_low = 1,
},
}
在初始化函数：ap121_setup 中，利用
ath79_register_gpio_keys_polled(-1, AP121_KEYS_POLL_INTERVAL,ARRAY_SIZE(ap121_gpio_keys),ap121_gpio_keys);
实现了KEY device的注册。此函数调用后，会创建platform类型的设备，并和gpio-keys-polled驱动(gpio-button-hotplug.c
)实现了绑定。
B.
当按键时，则触发button_hotplug_event函数（gpio-button-hotplug.c）：调用button_hotplug_create_event产生uevent事件，调用button_hotplug_fill_even填充事件(JSON格式)，并最终调用button_hotplug_work发出uevent广播
上述广播，被procd进程中的hotplug_handler (procd/plug/hotplug.c) 收到，并根据etc/hotplug.json中预先定义的JSON内容匹配条件，定位到对应的执行函数，具体为：
[ "if",
[ "and",
[ "has", "BUTTON" ],
[ "eq", "SUBSYSTEM", "button" ],
],
[ "exec", "/etc/rc.button/%BUTTON%" ]
],
和
[ "if",
[ "eq", "SUBSYSTEM",
[ "net", "input", "usb", "ieee1394", "block", "atm", "zaptel", "tty", "button" ]
],
[ "exec", "/sbin/hotplug-call", "%SUBSYSTEM%" ]
],