Linux Input子系统--设备的注册和打开

水平有限，描述不当之处还请指出，转载请注明出处http://blog.csdn.net/vanbreaker/article/details/7718158
这节结合even handler来分析设备的注册和打开的过程，在设备注册之前，必须先初始化INPUT子系统，由input_init()函数来完成

static int __init input_init(void)
{
	int err;

	input_init_abs_bypass();

	err = class_register(&input_class);//注册input类
	if (err) {
		printk(KERN_ERR "input: unable to register input_dev class\n");
		return err;
	}

	err = input_proc_init();//创建/proc中的项
	if (err)
		goto fail1;

	/*注册设备，设备号为INPUT_MAJOR(13),后面注册的输入设备都使用该主设备号*/
	err = register_chrdev(INPUT_MAJOR, "input", &input_fops);
	if (err) {
		printk(KERN_ERR "input: unable to register char major %d", INPUT_MAJOR);
		goto fail2;
	}

	return 0;

 fail2:	input_proc_exit();
 fail1:	class_unregister(&input_class);
	return err;
}

input_fops中只定义了open函数。

static const struct file_operations input_fops = {
	.owner = THIS_MODULE,
	.open = input_open_file,
};

我们需要在设备驱动层中完成输入设备的注册，通过调用input_register_device()函数来完成，该函数的一个重要任务就是完成设备与事件驱动的匹配。

int input_register_device(struct input_dev *dev)
{
	static atomic_t input_no = ATOMIC_INIT(0);
	struct input_handler *handler;
	const char *path;
	int error;

	__set_bit(EV_SYN, dev->evbit);

	/*
	 * If delay and period are pre-set by the driver, then autorepeating
	 * is handled by the driver itself and we don't do it in input.c.
	 */

	init_timer(&dev->timer);
	if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD]) {
		dev->timer.data = (long) dev;
		dev->timer.function = input_repeat_key;
		dev->rep[REP_DELAY] = 250;
		dev->rep[REP_PERIOD] = 33;
	}

	/*没有定义设备的getkeycode函数，则使用默认的获取键值函数*/
	if (!dev->getkeycode)
		dev->getkeycode = input_default_getkeycode;

	/*没有定义设备的setkeycode函数，则使用默认的设定键值函数*/
	if (!dev->setkeycode)
		dev->setkeycode = input_default_setkeycode;

	/*设定dev的名字*/
	dev_set_name(&dev->dev, "input%ld",
		     (unsigned long) atomic_inc_return(&input_no) - 1);

	/*添加设备*/
	error = device_add(&dev->dev);
	if (error)
		return error;

	path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
	printk(KERN_INFO "input: %s as %s\n",
		dev->name ? dev->name : "Unspecified device", path ? path : "N/A");
	kfree(path);

	error = mutex_lock_interruptible(&input_mutex);
	if (error) {
		device_del(&dev->dev);
		return error;
	}

	/*将设备添加到input_dev_list设备链表*/
	list_add_tail(&dev->node, &input_dev_list);

	/*遍历input_handler_list，试图与每一个handler进行匹配*/
	list_for_each_entry(handler, &input_handler_list, node)
		input_attach_handler(dev, handler);

	input_wakeup_procfs_readers();

	mutex_unlock(&input_mutex);

	return 0;
}

static int input_attach_handler(struct input_dev *dev, struct input_handler *handler)
{
	const struct input_device_id *id;
	int error;

	/*如果定义了handler的黑名单，并且设备和黑名单中的id匹配了，则该设备不能和handler匹配*/
	if (handler->blacklist && input_match_device(handler->blacklist, dev))
		return -ENODEV;

	id = input_match_device(handler->id_table, dev);
	if (!id)
		return -ENODEV;

	/*执行handler的connect,建立handler与设备之间的联系*/
	error = handler->connect(handler, dev, id);
	if (error && error != -ENODEV)
		printk(KERN_ERR
			"input: failed to attach handler %s to device %s, "
			"error: %d\n",
			handler->name, kobject_name(&dev->dev.kobj), error);

	return error;
}

匹配的具体过程：

static const struct input_device_id *input_match_device(const struct input_device_id *id,
							struct input_dev *dev)
{
	int i;

	/*遍历handler的id_table与device进行匹配*/
	for (; id->flags || id->driver_info; id++) {

		/*根据flags的标志位，按需要匹配相应的字段*/
		if (id->flags & INPUT_DEVICE_ID_MATCH_BUS)
			if (id->bustype != dev->id.bustype)//总线类型不匹配
				continue;

		if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR)//生产厂商不匹配
			if (id->vendor != dev->id.vendor)
				continue;

		if (id->flags & INPUT_DEVICE_ID_MATCH_PRODUCT)//产品不匹配
			if (id->product != dev->id.product)
				continue;

		if (id->flags & INPUT_DEVICE_ID_MATCH_VERSION)//版本不匹配
			if (id->version != dev->id.version)
				continue;
		
		MATCH_BIT(evbit,  EV_MAX);//匹配所有的事件类型

		/*匹配所有事件的子事件*/
		MATCH_BIT(keybit, KEY_MAX);
		MATCH_BIT(relbit, REL_MAX);
		MATCH_BIT(absbit, ABS_MAX);
		MATCH_BIT(mscbit, MSC_MAX);
		MATCH_BIT(ledbit, LED_MAX);
		MATCH_BIT(sndbit, SND_MAX);
		MATCH_BIT(ffbit,  FF_MAX);
		MATCH_BIT(swbit,  SW_MAX);

		return id;//匹配成功，返回id
	}

	return NULL;
}

MATCH_BIT是将device的相应字段和handler的相应字段逐位对比，都一样的话表示成功，否则continue

#define MATCH_BIT(bit, max) \
		for (i = 0; i < BITS_TO_LONGS(max); i++) \
			if ((id->bit[i] & dev->bit[i]) != id->bit[i]) \
				break; \
		if (i != BITS_TO_LONGS(max)) \
			continue;

以event handler为例，看connect函数做了什么：

static int evdev_connect(struct input_handler *handler, struct input_dev *dev,
			 const struct input_device_id *id)
{
	struct evdev *evdev;
	int minor;
	int error;

	/*在evdev_table中找到空闲块，其对应的数组下标再加上EVDEV_MINOR_BASE(64)就是次设备号
	  每个handler都拥有32个此设备号，也就是最多可以对应32个设备*/
	for (minor = 0; minor < EVDEV_MINORS; minor++)
		if (!evdev_table[minor])
			break;

	if (minor == EVDEV_MINORS) {
		printk(KERN_ERR "evdev: no more free evdev devices\n");
		return -ENFILE;
	}

	evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);
	if (!evdev)
		return -ENOMEM;

	INIT_LIST_HEAD(&evdev->client_list);
	spin_lock_init(&evdev->client_lock);
	mutex_init(&evdev->mutex);
	init_waitqueue_head(&evdev->wait);

	/*初始化evdev的内部变量*/
	snprintf(evdev->name, sizeof(evdev->name), "event%d", minor);
	evdev->exist = 1;
	evdev->minor = minor;

	/*初始化handle,每个evdev中都有一个handle*/
	evdev->handle.dev = input_get_device(dev);
	evdev->handle.name = evdev->name;
	evdev->handle.handler = handler;
	evdev->handle.private = evdev;

	/*初始化evdev中的内嵌device*/
	dev_set_name(&evdev->dev, evdev->name);
	evdev->dev.devt = MKDEV(INPUT_MAJOR, EVDEV_MINOR_BASE + minor);
	evdev->dev.class = &input_class;
	evdev->dev.parent = &dev->dev;
	evdev->dev.release = evdev_free;
	device_initialize(&evdev->dev);

	/*注册handle,主要将handle链接到input_dev和handler的h_list链表中去*/
	error = input_register_handle(&evdev->handle);
	if (error)
		goto err_free_evdev;

	/*将evdev存入evdev_table数组*/
	error = evdev_install_chrdev(evdev);
	if (error)
		goto err_unregister_handle;

	error = device_add(&evdev->dev);
	if (error)
		goto err_cleanup_evdev;

	return 0;

 err_cleanup_evdev:
	evdev_cleanup(evdev);
 err_unregister_handle:
	input_unregister_handle(&evdev->handle);
 err_free_evdev:
	put_device(&evdev->dev);
	return error;
}

至此设备的注册完成！对应event handler,在/dev中将多出一个event(x)设备文件，对应一个evdev实例，应用程序打开它的话也就意味着通过event handler来和设备驱动层传递事件。

再来看打开设备的过程，还是以event handler为例，假如打开一个event(x),则先执行：

static int input_open_file(struct inode *inode, struct file *file)
{
	struct input_handler *handler;
	const struct file_operations *old_fops, *new_fops = NULL;
	int err;

	lock_kernel();
	/* No load-on-demand here? */
	
	/*32个设备是共用一个handler的,通过此设备号得到设备对应的handler*/
	handler = input_table[iminor(inode) >> 5];
	if (!handler || !(new_fops = fops_get(handler->fops))) {
		err = -ENODEV;
		goto out;
	}

	/*
	 * That's _really_ odd. Usually NULL ->open means "nothing special",
	 * not "no device". Oh, well...
	 */
	if (!new_fops->open) {
		fops_put(new_fops);
		err = -ENODEV;
		goto out;
	}
	old_fops = file->f_op;
	/*定位fops*/
	file->f_op = new_fops;

	err = new_fops->open(inode, file);

	if (err) {
		fops_put(file->f_op);
		file->f_op = fops_get(old_fops);
	}
	fops_put(old_fops);
out:
	unlock_kernel();
	return err;
}

通过此设备号所在的组(0~31)，(32~63),(64~95)……就可以找到相应的handler，所有的handler都保存在input_table中，对于次设备号在64~95范围的设备，将定位到下标为2的handler,，也就是event handler，然后将用handler中的open函数替代之前的open函数，并执行新的open函数，这样就以handler本身定义的open来打开设备完成相应的初始化了。

event handler中的open函数：

static int evdev_open(struct inode *inode, struct file *file)
{
	struct evdev *evdev;
	struct evdev_client *client;
	int i = iminor(inode) - EVDEV_MINOR_BASE;
	int error;

	if (i >= EVDEV_MINORS)
		return -ENODEV;

	error = mutex_lock_interruptible(&evdev_table_mutex);
	if (error)
		return error;
	/*从evdev_table中取出和此设备号对应的evdev实例*/
	evdev = evdev_table[i];
	if (evdev)
		get_device(&evdev->dev);
	mutex_unlock(&evdev_table_mutex);

	if (!evdev)
		return -ENODEV;

	/*每当一个应用程序打开该文件都会生成一个client*/
	client = kzalloc(sizeof(struct evdev_client), GFP_KERNEL);
	if (!client) {
		error = -ENOMEM;
		goto err_put_evdev;
	}

	spin_lock_init(&client->buffer_lock);
	client->evdev = evdev;
	/*将client链入evdev的client_list中*/
	evdev_attach_client(evdev, client);

	error = evdev_open_device(evdev);
	if (error)
		goto err_free_client;

	file->private_data = client;
	return 0;

 err_free_client:
	evdev_detach_client(evdev, client);
	kfree(client);
 err_put_evdev:
	put_device(&evdev->dev);
	return error;
}

static int evdev_open_device(struct evdev *evdev)
{
	int retval;

	retval = mutex_lock_interruptible(&evdev->mutex);
	if (retval)
		return retval;

	if (!evdev->exist)
		retval = -ENODEV;
	else if (!evdev->open++) {/*如果是第一次打开该设备，则要执行设备中定义的open*/
		retval = input_open_device(&evdev->handle);
		if (retval)
			evdev->open--;
	}

	mutex_unlock(&evdev->mutex);
	return retval;
}

int input_open_device(struct input_handle *handle)
{
	struct input_dev *dev = handle->dev;
	int retval;

	retval = mutex_lock_interruptible(&dev->mutex);
	if (retval)
		return retval;

	if (dev->going_away) {
		retval = -ENODEV;
		goto out;
	}

	handle->open++;

	if (!dev->users++ && dev->open)
		retval = dev->open(dev);//执行input_dev中定义的open，完成设备的初始化

	if (retval) {
		dev->users--;
		if (!--handle->open) {
			/*
			 * Make sure we are not delivering any more events
			 * through this handle
			 */
			synchronize_rcu();
		}
	}

 out:
	mutex_unlock(&dev->mutex);
	return retval;
}