Linux下LED子系统分析

Linux下LED子系统分析

本文基于Linux Kernel3.0.8版本

一、主要文件和结构

linux的led子系统的源码路径

include/Linux/leds.h
drivers/leds/*

从drivers/leds/Makefile中可以看到LED子系统的主要文件有几类：
LED核心：leds.h、led-core.c、led-class.c、led-triggers.c（其中led-triggers又分为了timer、ide-disk、heartbeat、backlight、gpio、default-on等）
应用LED的各种Drivers：基于Platform平台总线，SPI总线的应用

# LED Core
obj-$(CONFIG_NEW_LEDS)         += led-core.o
obj-$(CONFIG_LEDS_CLASS)       += led-class.o
obj-$(CONFIG_LEDS_TRIGGERS)        += led-triggers.o

# LED Platform Drivers
......
obj-$(CONFIG_LEDS_GPIO)            += leds-gpio.o
......

# LED SPI Drivers
obj-$(CONFIG_LEDS_DAC124S085)      += leds-dac124s085.o

# LED Triggers
obj-$(CONFIG_LEDS_TRIGGER_TIMER)   += ledtrig-timer.o
obj-$(CONFIG_LEDS_TRIGGER_IDE_DISK)    += ledtrig-ide-disk.o
obj-$(CONFIG_LEDS_TRIGGER_HEARTBEAT)   += ledtrig-heartbeat.o
obj-$(CONFIG_LEDS_TRIGGER_BACKLIGHT)   += ledtrig-backlight.o
obj-$(CONFIG_LEDS_TRIGGER_GPIO)        += ledtrig-gpio.o
obj-$(CONFIG_LEDS_TRIGGER_DEFAULT_ON)  += ledtrig-default-on.o
obj-$(CONFIG_LEDS_TRIGGER_SLEEP)   += ledtrig-sleep.o

include/linux/leds.h

//Led的亮度，分为三等级，关、中间、最亮。
enum led_brightness {
    LED_OFF     = 0,
#if defined(CONFIG_MACH_Q1_BD)   || defined(CONFIG_MACH_U1_NA_USCC)
    LED_BRIGHTNESS_LEVEL1   = 1,
    LED_BRIGHTNESS_LEVEL2   = 2,
    LED_BRIGHTNESS_LEVEL3   = 3,
    LED_BRIGHTNESS_MAX_LEVEL    = LED_BRIGHTNESS_LEVEL3,
#endif
    LED_HALF    = 127,
    LED_FULL    = 255,
};

led_classdev 结构：

struct led_classdev {
    const char      *name;  // Led的名字  
    int          brightness; //Led亮度
    int          max_brightness; //led最大亮度 
    int          flags;

    /* Lower 16 bits reflect status */
#define LED_SUSPENDED       (1 << 0)
    /* Upper 16 bits reflect control information */
#define LED_CORE_SUSPENDRESUME  (1 << 16)

    /* Set LED brightness level */
    /* Must not sleep, use a workqueue if needed */
    void        (*brightness_set)(struct led_classdev *led_cdev,
                      enum led_brightness brightness); // 用于设置亮度的函数指针
    /* Get LED brightness level */
    enum led_brightness (*brightness_get)(struct led_classdev *led_cdev); // 用于获取亮度的函数指针

    /*
     * Activate hardware accelerated blink, delays are in milliseconds
     * and if both are zero then a sensible default should be chosen.
     * The call should adjust the timings in that case and if it can't
     * match the values specified exactly.
     * Deactivate blinking again when the brightness is set to a fixed
     * value via the brightness_set() callback.
     */
    int     (*blink_set)(struct led_classdev *led_cdev,
                     unsigned long *delay_on,
                     unsigned long *delay_off); // 用来设置闪烁时点亮和熄灭时长

    struct device       *dev;
    struct list_head     node;          /* LED Device list LED设备链表 */
    const char      *default_trigger;   /* Trigger to use 该led_classdev使用的trigger的名字,通过这个名字在trigger_list中找到对应的trigger */

    unsigned long        blink_delay_on, blink_delay_off; // 闪烁的开关时间
    struct timer_list    blink_timer; // 闪烁的定时器链表
    int          blink_brightness; // 闪烁的亮度

#ifdef CONFIG_LEDS_TRIGGERS
    /* Protects the trigger data below */
    struct rw_semaphore  trigger_lock; // trigger的锁

    struct led_trigger  *trigger; // Led的trigger
    struct list_head     trig_list; // trigger链表
    void            *trigger_data; // trigger数据
#endif
}

led_trigger 结构：

struct led_trigger {
    /* Trigger Properties */
    const char   *name; //trigger的名字 
    void        (*activate)(struct led_classdev *led_cdev); //激活trigger
    void        (*deactivate)(struct led_classdev *led_cdev); //关闭trigger

    /* LEDs under control by this trigger (for simple triggers) */
    rwlock_t      leddev_list_lock;
    struct list_head  led_cdevs;  // 该trigger支持的led设备链表 

    /* Link to next registered trigger */
    struct list_head  next_trig;
};

gpio_led 结构适用于leds-gpio.c：

/* For the leds-gpio driver */
struct gpio_led {
    const char *name; //led的名字
    const char *default_trigger; //默认的trigger  
    unsigned    gpio; //gpio口 
    unsigned    active_low : 1;
    unsigned    retain_state_suspended : 1;
    unsigned    default_state : 2;
    /* default_state should be one of LEDS_GPIO_DEFSTATE_(ON|OFF|KEEP) */
};

struct gpio_led_platform_data {
    int         num_leds; //led的个数 
    const struct gpio_led *leds; //led结构体 

#define GPIO_LED_NO_BLINK_LOW   0   /* No blink GPIO state low */
#define GPIO_LED_NO_BLINK_HIGH  1   /* No blink GPIO state high */
#define GPIO_LED_BLINK      2   /* Please, blink */
    int     (*gpio_blink_set)(unsigned gpio, int state,
                    unsigned long *delay_on,
                    unsigned long *delay_off);
};

led-core.c

声明了leds的链表和锁

DECLARE_RWSEM(leds_list_lock);
EXPORT_SYMBOL_GPL(leds_list_lock);

LIST_HEAD(leds_list);
EXPORT_SYMBOL_GPL(leds_list);

led-class.c

1. leds_init
   创建leds class，赋值suspend和resume以及dev_attrs。

static int __init leds_init(void)
{
    leds_class = class_create(THIS_MODULE, "leds"); // /sys/class/leds/
    if (IS_ERR(leds_class))
        return PTR_ERR(leds_class);
    leds_class->suspend = led_suspend;
    leds_class->resume = led_resume;
    leds_class->dev_attrs = led_class_attrs;
    return 0;
}

led_class_attrs里面可以设置各项属性的权限，每个属性对应leds class底下的一个文件，应用程序去read属性文件时，会调用到show函数（比如brightness的led_brightness_show），应用程序去write属性文件时，会调用到store函数（比如brightness的led_brightness_store）

static struct device_attribute led_class_attrs[] = {
    // /sys/class/leds/brightnes