android button light 流程分析(一) — driver

最新推荐文章于 2021-05-29 10:15:27 发布

g_salamander

最新推荐文章于 2021-05-29 10:15:27 发布

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分类专栏：源码分析文章标签： button android struct delay module list

本文链接：https://blog.youkuaiyun.com/g_salamander/article/details/7946026

本文探讨了Android button light driver的核心层——led-class，它管理系统所有的LED，并提供了设置亮度、获取亮度等接口。重点讲解了led-trigger，即触发器的概念，用户可以通过触发器控制LED的亮灭。此外，文章指出在timer触发器中直接设置亮度可能导致问题，建议使用工作队列以避免内核崩溃。

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一、led-class

led-class是button light driver的核心层，代码位于drivers/leds/目录下，提供了一些数据结构和接口，其中创建了一个leds设备类，用于管理系统所有的led，代码如下：

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;
	return 0;
}

static void __exit leds_exit(void)
{
	class_destroy(leds_class);
}

subsys_initcall(leds_init);
module_exit(leds_exit);

创建成功后我们可以在/sys/class目录下面看到leds目录，并注册了统一的休眠和唤醒函数：

/**
 * led_classdev_suspend - suspend an led_classdev.
 * @led_cdev: the led_classdev to suspend.
 */
void led_classdev_suspend(struct led_classdev *led_cdev)
{
	led_cdev->flags |= LED_SUSPENDED;
	led_cdev->brightness_set(led_cdev, 0);
}
EXPORT_SYMBOL_GPL(led_classdev_suspend);

/**
 * led_classdev_resume - resume an led_classdev.
 * @led_cdev: the led_classdev to resume.
 */
void led_classdev_resume(struct led_classdev *led_cdev)
{
	led_cdev->brightness_set(led_cdev, led_cdev->brightness);
	led_cdev->flags &= ~LED_SUSPENDED;
}
EXPORT_SYMBOL_GPL(led_classdev_resume);

static int led_suspend(struct device *dev, pm_message_t state)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);

	if (led_cdev->flags & LED_CORE_SUSPENDRESUME)
		led_classdev_suspend(led_cdev);

	return 0;
}

static int led_resume(struct device *dev)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);

	if (led_cdev->flags & LED_CORE_SUSPENDRESUME)
		led_classdev_resume(led_cdev);

	return 0;
}

suspend主要设置一下标志并将led关闭，resume主要清除标志并将led恢复之前亮度。同时led-class提供了结构体led_classdev作为统一的led设备模型：

struct led_classdev {
	const char		*name;
	int			 brightness;
	int			 max_brightness;
	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);
	/* Get LED brightness level */
	enum led_brightness (*brightness_get)(struct led_classdev *led_cdev);

	/* 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;
	struct list_head	 node;			/* LED Device list */
	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
};

其中提供了设置亮度、获取亮度、闪烁led几个接口、还有trigger域以及相关链表节点。在led-class中还定义了brightness、max_brightness两个属性提供给HAL层使用：

static void led_update_brightness(struct led_classdev *led_cdev)
{
	if (led_cdev->brightness_get)
		led_cdev->brightness = led_cdev->brightness_get(led_cdev);
}

static ssize_t led_brightness_show(struct device *dev, 
		struct device_attribute *attr, char *buf)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);

	/* no lock needed for this */
	led_update_brightness(led_cdev);

	return sprintf(buf, "%u\n", led_cdev->brightness);
}

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);
	ssize_t ret = -EINVAL;
	char *after;
	unsigned long state = simple_strtoul(buf, &after, 10);
	size_t count = after - buf;

	if (*after && 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;
}

static ssize_t led_max_brightness_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct led_classdev *led_cdev = dev_get_drvdata(dev);

	return sprintf(buf, "%u\n", led_cdev->max_brightness);
}

static DEVICE_ATTR(brightness, 0644, led_brightness_show, led_brightness_store);
static DEVICE_ATTR(max_brightness, 0444, led_max_brightness_show, NULL);

其中brightness主要用于设置和读取亮度值，max_brightness则用于读取硬件支持的最大亮度值。led-class还提供了注册led_classdev的统一接口：

/**
 * led_classdev_register - register a new object of led_classdev class.
 * @parent: The device to register.
 * @led_cdev: the led_classdev structure for this device.
 */
int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
{