linux驱动之input子系统

一、input子系统简述

在我们的平常使用的电子设备中，比如鼠标，键盘，案件，游戏手柄等在linux的世界中华都是属于input设备。
在android的kernel中，sensor，key，touch等都是以input方式给hal层提供相关的接口。
所以input子系统在内核中有着很重要的地位，使得运用程序只需要读取/dev/inputx就可以完成对硬件的数据读取。

二、从示例中学习input

先前写过一个input相关，但是发现kernel版本太旧了，已经不合适新的input了，查看新的kernel之后发现了有较大的改动，所以就删掉原来的input相关，察觉到从实际例子中分析便以大家去理解input子系统。
学习input子系统，我们只需要掌握三个数据结构，分别为：
1、struct input_dev
2、struct input_handler
3、struct input_hand
我们开始吧！！！
在drivers\input\touchscreen\s3c2410_ts.c 这是一个很久的片子了，但是它的代码依旧还在内核中，而且是一个不错的例子
probe开始吧：

2.1、在drivers/input/input.c中，可以看到input的入口、

static int s3c2410ts_probe(struct platform_device *pdev)
{
	struct s3c2410_ts_mach_info *info;
	struct device *dev = &pdev->dev;
	struct input_dev *input_dev;
	struct resource *res;
	int ret = -EINVAL;
	ts.input = input_dev;
	ts.input->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
	ts.input->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
	input_set_abs_params(ts.input, ABS_X, 0, 0x3FF, 0, 0);
	input_set_abs_params(ts.input, ABS_Y, 0, 0x3FF, 0, 0);

	input_dev = input_allocate_device();
	ts.input = input_dev;
	ts.input->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
	ts.input->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
	input_set_abs_params(ts.input, ABS_X, 0, 0x3FF, 0, 0);
	input_set_abs_params(ts.input, ABS_Y, 0, 0x3FF, 0, 0);
	
	ts.input->name = "S3C24XX TouchScreen";
	ts.input->id.bustype = BUS_HOST;
	ts.input->id.vendor = 0xDEAD;
	ts.input->id.product = 0xBEEF;
	ts.input->id.version = 0x0102;

	ts.shift = info->oversampling_shift;
	ts.features = platform_get_device_id(pdev)->driver_data;

	/* All went ok, so register to the input system */
	ret = input_register_device(ts.input);
	if (ret < 0) {
		dev_err(dev, "failed to register input device\n");
		ret = -EIO;
		goto err_tcirq;
	}
	return 0;
}

老规矩，无相关的代码依旧被我删掉了，碍眼、
看到了我们第一个数据结构相关的函数了没？ 没错，就是 *input_register_device(struct input_dev dev) 这货了。

int input_register_device(struct input_dev *dev)
{
	struct input_devres *devres = NULL;
	struct input_handler *handler;
	unsigned int packet_size;
	const char *path;
	int error;

	if (dev->devres_managed) {
		devres = devres_alloc(devm_input_device_unregister,
				      sizeof(struct input_devres), GFP_KERNEL);
		if (!devres)
			return -ENOMEM;

		devres->input = dev;
	}

	/* Every input device generates EV_SYN/SYN_REPORT events. */
	__set_bit(EV_SYN, dev->evbit);

	/* KEY_RESERVED is not supposed to be transmitted to userspace. */
	__clear_bit(KEY_RESERVED, dev->keybit);

	/* Make sure that bitmasks not mentioned in dev->evbit are clean. */
	input_cleanse_bitmasks(dev);

	packet_size = input_estimate_events_per_packet(dev);
	if (dev->hint_events_per_packet < packet_size)
		dev->hint_events_per_packet = packet_size;

	dev->max_vals = dev->hint_events_per_packet + 2;
	dev->vals = kcalloc(dev->max_vals, sizeof(*dev->vals), GFP_KERNEL);
	if (!dev->vals) {
		error = -ENOMEM;
		goto err_devres_free;
	}
	/*
	 * 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.
	 */
	if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD])
		input_enable_softrepeat(dev, 250, 33);

	if (!dev->getkeycode)
		dev->getkeycode = input_default_getkeycode;

	if (!dev->setkeycode)
		dev->setkeycode = input_default_setkeycode;

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

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

	error = mutex_lock_interruptible(&input_mutex);
	if (error)
		goto err_device_del;

	list_add_tail(&dev->node, &input_dev_list);

	list_for_each_entry(handler, &input_handler_list, node)
		input_attach_handler(dev, handler);

	input_wakeup_procfs_readers();

	mutex_unlock(&input_mutex);

	if (dev->devres_managed) {
		dev_dbg(dev->dev.parent, "%s: registering %s with devres.\n",
			__func__, dev_name(&dev->dev));
		devres_add(dev->dev.parent, devres);
	}
	return 0;
}

不知道大家注意了吗？？ 整个函数就一端比较有用的就是：
list_add_tail(&dev->node, &input_dev_list);
list_for_each_entry(handler, &input_handler_list, node)
input_attach_handler(dev, handler);

就是他了，将我们注册的input_dev挂接到input_dev_list这个链表上，然后去遍历链表input_handler_list，取出handler，

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

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

	error = handler->connect(handler, dev, id);
	if (error && error != -ENODEV)
		pr_err("failed to attach handler %s to device %s, error: %d\n",
		       handler->name, kobject_name(&dev->dev.kobj), error);

	return error;
}

上面的attach函数是不是有点platform的味道了。

static const struct input_device_id *input_match_device(struct input_handler *handler,
							struct input_dev *dev)
{
	const struct input_device_id *id;

	for (id = handler->id_table; id->flags || id->driver_info; id++) {
		/*这堆东西很重要，作为dev与handler的匹配项*/
		if (id->flags & INPUT_DEVICE_ID_MATCH_BUS)
			if (id->bustype != dev->id.bustype)
				continue;

		if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR)
			if (id->vendor != dev->id.vendor)
				continue;

		if (id->flags & INPUT_DEVICE_ID_MATCH_PRODUCT)
			if (id->product != dev->id.product)
				continue;

		if (id->flags & INPUT_DEVICE_ID_MATCH_VERSION)
			if (id->version != dev->id.version)
				continue;

		if (!bitmap_subset(id->evbit, dev->evbit, EV_MAX))
			continue;

		if (!bitmap_subset(id->keybit, dev->keybit, KEY_MAX))
			continue;

		if (!bitmap_subset(id->relbit, dev->relbit, REL_MAX))
			continue;

		if (!bitmap_subset(id->absbit, dev->absbit, ABS_MAX))
			continue;

		if (!bitmap_subset(id->mscbit, dev->mscbit, MSC_MAX))
			continue;

		if (!bitmap_subset(id->ledbit, dev->ledbit, LED_MAX))
			continue;

		if (!bitmap_subset(id->sndbit, dev->sndbit, SND_MAX))
			continue;

		if (!bitmap_subset(id->ffbit, dev->ffbit, FF_MAX))
			continue;

		if (!bitmap_subset(id->swbit, dev->swbit, SW_MAX))
			continue;

		if (!handler->match || handler->match(handler, dev))
			return id;
	}
	return NULL;
}

有点长，但是我们重点关注最后一句就好了，
但是。。。。？ 我们只是注册了input_dev这个dev，需要的handler从什么地方来的

继续在input中搜索input_handler_list这个链表，果不其然，发现了
int input_register_handler(struct input_handler *handler) 这个函数，看看什么地方调用了这个接口勒

哈哈哈：在evdev.c中作为入口函数中调用了。

static int __init evdev_init(void)
{
	return input_register_handler(&evdev_handler);
}

继续：

static struct input_handler evdev_handler = {
	.event		= evdev_event,
	.events		= evdev_events,
	.connect	= evdev_connect,
	.disconnect	= evdev_disconnect,
	.legacy_minors	= true,
	.minor		= EVDEV_MINOR_BASE,
	.name		= "evdev",
	.id_table	= evdev_ids,
};

不知道大家是否还记得input_match_device()这个注册dev时候的匹配函数勒。

```c
static const struct input_device_id evdev_ids[] = {
	{ .driver_info = 1 },	/* Matches all devices */
	{ },			/* Terminating zero entry */
};

input使用全匹配方式，
当dev与handler匹配成功后，会调用handler->connect函数，还记得吧、

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

	minor = input_get_new_minor(EVDEV_MINOR_BASE, EVDEV_MINORS, true);
	if (minor < 0) {
		error = minor;
		pr_err("failed to reserve new minor: %d\n", error);
		return error;
	}

	evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);
	if (!evdev) {
		error = -ENOMEM;
		goto err_free_minor;
	}

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

	dev_no = minor;
	/* Normalize device number if it falls into legacy range */
	if (dev_no < EVDEV_MINOR_BASE + EVDEV_MINORS)
		dev_no -= EVDEV_MINOR_BASE;
	dev_set_name(&evdev->dev, "event%d", dev_no);

	evdev->handle.dev = input_get_device(dev);
	evdev->handle.name = dev_name(&evdev->dev);
	evdev->handle.handler = handler;
	evdev->handle.private = evdev;

	evdev->dev.devt = MKDEV(INPUT_MAJOR, minor);
	evdev->dev.class = &input_class;
	evdev->dev.parent = &dev->dev;
	evdev->dev.release = evdev_free;
	device_initialize(&evdev->dev);

	error = input_register_handle(&evdev->handle);
	if (error)
		goto err_free_evdev;

	cdev_init(&evdev->cdev, &evdev_fops);
	evdev->cdev.kobj.parent = &evdev->dev.kobj;
	error = cdev_add(&evdev->cdev, evdev->dev.devt, 1);
	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);
 err_free_minor:
	input_free_minor(minor);
	return error;
}

哎呦喂，手都敲坏了，终于到最后一个重要的数据结构了。
input_register_handle(&evdev->handle);就是这货的handle了。

int input_register_handle(struct input_handle *handle)
{
	struct input_handler *handler = handle->handler;
	struct input_dev *dev = handle->dev;
	int error;

	/*
	 * We take dev->mutex here to prevent race with
	 * input_release_device().
	 */
	error = mutex_lock_interruptible(&dev->mutex);
	if (error)
		return error;

	/*
	 * Filters go to the head of the list, normal handlers
	 * to the tail.
	 */
	if (handler->filter)
		list_add_rcu(&handle->d_node, &dev->h_list);
	else
		list_add_tail_rcu(&handle->d_node, &dev->h_list);

	mutex_unlock(&dev->mutex);

	/*
	 * Since we are supposed to be called from ->connect()
	 * which is mutually exclusive with ->disconnect()
	 * we can't be racing with input_unregister_handle()
	 * and so separate lock is not needed here.
	 */
	list_add_tail_rcu(&handle->h_node, &handler->h_list);

	if (handler->start)
		handler->start(handle);

	return 0;
}

这个函数主要是将handle与input_dev进行数据链接。
然后将相关联的数据以字符设备的方式注册到文件系统中，这就是完成了整个input的流程了。
概念讲完了，驱动很简单，就不写了。
大家再见。。。。。。