linux设备模型之led子系统
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时代不同了，连led都成子系统了，针对内核提供的通用模型，分析一下，好久没写文章了也！
代码位于drivers/leds下，看一下Makefile 模型文件主要是：
# LED Core
obj-$(CONFIG_NEW_LEDS) += led-core.o
obj-$(CONFIG_LEDS_CLASS) += led-class.o
obj-$(CONFIG_LEDS_TRIGGERS) += led-triggers.o
直接看led-core文件吧，这个文件无比个性，主体内容四行
DECLARE_RWSEM(leds_list_lock);
EXPORT_SYMBOL_GPL(leds_list_lock);
LIST_HEAD(leds_list); //链接所有led的全局链表
EXPORT_SYMBOL_GPL(leds_list);
再来看下led-class.c函数，这里先来介绍一下描述led的核心结构体
struct led_classdev {
const char *name; //名字
int brightness; //亮度值，也可以用来表示开关特性
int max_brightness; //允许的最大亮度值
int flags; //标志
/* 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, //核心回调函数，当设置/sys/class/leds/下的led接口里的brightness属性文件时，会回调该函数
enum led_brightness brightness);
/* Get LED brightness level */
enum led_brightness (*brightness_get)(struct led_classdev *led_cdev); //核心回调函数，当获得led当前值时会调用
/* Activate hardware accelerated blink, delays are in
* miliseconds and if none is provided then a sensible default
* should be chosen. The call can adjust the timings if it can't
* match the values specified exactly. */
int (*blink_set)(struct led_classdev *led_cdev,
unsigned long *delay_on,
unsigned long *delay_off);
struct device *dev; //嵌入的标准设备模型
struct list_head node; /* LED Device list */ //上面提到的全局led设备的挂接点
const char *default_trigger; /* Trigger to use */
#ifdef CONFIG_LEDS_TRIGGERS
/* Protects the trigger data below */
struct rw_semaphore trigger_lock;
struct led_trigger *trigger;
struct list_head trig_list;
void *trigger_data;
#endif
};
好了，下面说下初始化函数：
static int __init leds_init(void)
{
leds_class = class_create(THIS_MODULE, "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; //属性文件，sys下的接口，重点看一下
return 0;
}
函数在/sys/class目录下产生了leds这个子目录，按照led模型注册的设备都会出现在该目录下
static struct device_attribute led_class_attrs[] = {
__ATTR(brightness, 0644, led_brightness_show, led_brightness_store),
__ATTR(max_brightness, 0644, led_max_brightness_show,
led_max_brightness_store),
#ifdef CONFIG_LEDS_TRIGGERS
__ATTR(trigger, 0644, led_trigger_show, led_trigger_store),
#endif
__ATTR_NULL,
};
可见，属性函数的通用设置函数为led_brightness_store，获得函数位led_brightness_show，大同小异：
static ssize_t led_brightness_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t size)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev); //获得led设备信息
ssize_t ret = -EINVAL;
char *after;
unsigned long state = simple_strtoul(buf, &after, 10);
size_t count = after - buf;
if (isspace(*after))
count++;
if (count == size) {
ret = count;
if (state == LED_OFF)
led_trigger_remove(led_cdev);
led_set_brightness(led_cdev, state);
}
return ret;
}
跟进一下led_set_brightness函数：
static inline void led_set_brightness(struct led_classdev *led_cdev,
enum led_brightness value)
{
if (value > led_cdev->max_brightness)
value = led_cdev->max_brightness;
led_cdev->brightness = value;
if (!(led_cdev->flags & LED_SUSPENDED)) {
#ifdef CONFIG_HAS_EARLYSUSPEND
if (queue_brightness_change(led_cdev, value) != 0)
#endif
led_cdev->brightness_set(led_cdev, value);
}
}
可见最终确实是回调的 led_cdev->brightness_set来完成的该属性的设置。
下面看一下给我们留的接口，注册函数：
int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
{
led_cdev->dev = device_create(leds_class, parent, 0, led_cdev,
"%s", led_cdev->name); //在leds目录下产生该设备的目录项
if (IS_ERR(led_cdev->dev))
return PTR_ERR(led_cdev->dev);
#ifdef CONFIG_LEDS_TRIGGERS
init_rwsem(&led_cdev->trigger_lock);
#endif
/* add to the list of leds */
down_write(&leds_list_lock);
list_add_tail(&led_cdev->node, &leds_list); //把该设备加入全局链表
up_write(&leds_list_lock);
if (!led_cdev->max_brightness)
led_cdev->max_brightness = LED_FULL; //最大值如果没设置，则设置成255
led_update_brightness(led_cdev);
#ifdef CONFIG_LEDS_TRIGGERS
led_trigger_set_default(led_cdev);
#endif
printk(KERN_DEBUG "Registered led device: %s\n",
led_cdev->name);
return 0;
}
总结：基本上简要分析了一下led子系统，代码不多，也很容易看，主要自己端的probe函数要配置好io口的功能，填充好led_cdev这个东东，然后注册就可以了 ^.^~
