输入子系统--event层分析『转』

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早前曾研究了一下输入子系统的原理,给人的感觉是输入子系统很复杂.但其实内核开发者在这方面已经做得很完善了,
输入子系统虽然错综复杂,但是只要我们领会了输入子系统的一些设计思想后,我们要使用它并非难事.

以下以内核自带的gpio_keys驱动为例,介绍输入子系统的使用.
主要的原因是gpio_keys驱动比较简单易懂,另外不是没个人都有触摸屏,但键盘的话相信每一块开发板上都配有吧^_^

按照以前的习惯,先从下到上的研究底层驱动是如何提交输入事件的:
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drivers/input/keyboard/gpio_keys.c:

static int __devinit gpio_keys_probe(struct platform_device *pdev)
{
struct gpio_keys_platform_data *pdata = pdev->dev.platform_data;
struct input_dev *input;
int i, error;

input = input_allocate_device();//申请input_dev结构
if (!input)
return -ENOMEM;

platform_set_drvdata(pdev, input);//把input_dev结构放好(以后方便调用)

input->evbit[0] = BIT(EV_KEY);//目前event的类型不操作32,所以你会看到对于evbit数组的操作都是对evbit[0]中的位来进行操作.

input->name = pdev->name;
input->phys = "gpio-keys/input0";
input->dev.parent = &pdev->dev;

input->id.bustype = BUS_HOST;
input->id.vendor = 0x0001;
input->id.product = 0x0001;
input->id.version = 0x0100;

for (i = 0; i <>nbuttons; i++) {
struct gpio_keys_button *button = &pdata->buttons[i];
int irq = gpio_to_irq(button->gpio);
unsigned int type = button->type ?: EV_KEY;

set_irq_type(irq, IRQ_TYPE_EDGE_BOTH);

/* 根据用户所指定的gpio_keys来申请中断和注册中断处理函数*/
error = request_irq(irq, gpio_keys_isr, IRQF_SAMPLE_RANDOM,
button->desc ? button->desc : "gpio_keys",
pdev);
if (error) {
printk(KERN_ERR "gpio-keys: unable to claim irq %d; error %d\n",
irq, error);
goto fail;
}

input_set_capability(input, type, button->code);
}

error = input_register_device(input);//注册输入设备,并和对应的handler处理函数挂钩
if (error) {
printk(KERN_ERR "Unable to register gpio-keys input device\n");
goto fail;
}

return 0;

fail:
for (i = i - 1; i >= 0; i--)
free_irq(gpio_to_irq(pdata->buttons[i].gpio), pdev);

input_free_device(input);

return error;
}


提到input_dev结构,以下谈一下我对于它的理解:
struct input_dev {

void *private;

const char *name;
const char *phys;
const char *uniq;
struct input_id id;

/*
* 根据各种输入信号的类型来建立类型为unsigned long 的数组,
* 数组的每1bit代表一种信号类型,
* 内核中会对其进行置位或清位操作来表示时间的发生和被处理.
*/

unsigned long evbit[NBITS(EV_MAX)];
unsigned long keybit[NBITS(KEY_MAX)];
unsigned long relbit[NBITS(REL_MAX)];
unsigned long absbit[NBITS(ABS_MAX)];
unsigned long mscbit[NBITS(MSC_MAX)];
unsigned long ledbit[NBITS(LED_MAX)];
unsigned long sndbit[NBITS(SND_MAX)];
unsigned long ffbit[NBITS(FF_MAX)];
unsigned long swbit[NBITS(SW_MAX)];

.........................................
};

/**
* input_set_capability - mark device as capable of a certain event
* @dev: device that is capable of emitting or accepting event
* @type: type of the event (EV_KEY, EV_REL, etc...)
* @code: event code
*
* In addition to setting up corresponding bit in appropriate capability
* bitmap the function also adjusts dev->evbit.
*/

/* 记录本设备对于哪些事件感兴趣(对其进行处理)*/
void input_set_capability(struct input_dev *dev, unsigned int type, unsigned int code)
{
switch (type) {
case EV_KEY:
__set_bit(code, dev->keybit);//比如按键,应该对哪些键值的按键进行处理(对于其它按键不予理睬)
break;

case EV_REL:
__set_bit(code, dev->relbit);
break;

case EV_ABS:
__set_bit(code, dev->absbit);
break;

case EV_MSC:
__set_bit(code, dev->mscbit);
break;

case EV_SW:
__set_bit(code, dev->swbit);
break;

case EV_LED:
__set_bit(code, dev->ledbit);
break;

case EV_SND:
__set_bit(code, dev->sndbit);
break;

case EV_FF:
__set_bit(code, dev->ffbit);
break;

default:
printk(KERN_ERR
"input_set_capability: unknown type %u (code %u)\n",
type, code);
dump_stack();
return;
}

__set_bit(type, dev->evbit);//感觉和前面重复了(前面一经配置过一次了)
}
EXPORT_SYMBOL(input_set_capability);


static irqreturn_t gpio_keys_isr(int irq, void *dev_id)
{
int i;
struct platform_device *pdev = dev_id;
struct gpio_keys_platform_data *pdata = pdev->dev.platform_data;
struct input_dev *input = platform_get_drvdata(pdev);

for (i = 0; i <>nbuttons; i++) {
struct gpio_keys_button *button = &pdata->buttons[i];
int gpio = button->gpio;

if (irq == gpio_to_irq(gpio)) {//判断哪个键被按了?
unsigned int type = button->type ?: EV_KEY;
int state = (gpio_get_value(gpio) ? 1 : 0) ^ button->active_low;//记录按键状态

input_event(input, type, button->code, !!state);//汇报输入事件
input_sync(input);//等待输入事件处理完成
}
}

return IRQ_HANDLED;
}


/*
* input_event() - report new input event
* @dev: device that generated the event
* @type: type of the event
* @code: event code
* @value: value of the event
*
* This function should be used by drivers implementing various input devices
* See also input_inject_event()
*/
void input_event(struct input_dev *dev, unsigned int type, unsigned int code, int value)
{
struct input_handle *handle;

if (type > EV_MAX || !test_bit(type, dev->evbit))//首先判断该事件类型是否有效且为该设备所接受
return;

add_input_randomness(type, code, value);

switch (type) {

case EV_SYN:
switch (code) {
case SYN_CONFIG:
if (dev->event)
dev->event(dev, type, code, value);
break;

case SYN_REPORT:
if (dev->sync)
return;
dev->sync = 1;
break;
}
break;

case EV_KEY:
/*
* 这里需要满足几个条件:
* 1: 键值有效(不超出定义的键值的有效范围)
* 2: 键值为设备所能接受(属于该设备所拥有的键值范围)
* 3: 按键状态改变了
*/

if (code > KEY_MAX || !test_bit(code, dev->keybit) || !!test_bit(code, dev->key) == value)
return;

if (value == 2)
break;

change_bit(code, dev->key);//改变对应按键的状态

/* 如果你希望按键未释放的时候不断汇报按键事件的话需要以下这个(在简单的gpio_keys驱动中不需要这个,暂时不去分析) */
if (test_bit(EV_REP, dev->evbit) && dev->rep[REP_PERIOD] && dev->rep[REP_DELAY] && dev->timer.data && value) {
dev->repeat_key = code;
mod_timer(&dev->timer, jiffies + msecs_to_jiffies(dev->rep[REP_DELAY]));
}

break;
........................................................

if (type != EV_SYN)
dev->sync = 0;

if (dev->grab)
dev->grab->handler->event(dev->grab, type, code, value);
else
/*
* 循环调用所有处理该设备的handle(event,mouse,ts,joy等),
* 如果有进程打开了这些handle(进行读写),则调用其对应的event接口向气汇报该输入事件.
*/
list_for_each_entry(handle, &dev->h_list, d_node)
if (handle->open)
handle->handler->event(handle, type, code, value);
}
EXPORT_SYMBOL(input_event);


#########################################################################
好了,下面再来研究一下event层对于input层报告的这个键盘输入事件是如何来处理的.
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drivers/input/evdev.c:

static struct input_handler evdev_handler = {
.event = evdev_event,
.connect = evdev_connect,
.disconnect = evdev_disconnect,
.fops = &evdev_fops,
.minor = EVDEV_MINOR_BASE,
.name = "evdev",
.id_table = evdev_ids,
};

static void evdev_event(struct input_handle *handle, unsigned int type, unsigned int code, int value)
{
struct evdev *evdev = handle->private;
struct evdev_client *client;

if (evdev->grab) {
client = evdev->grab;

do_gettimeofday(&client->buffer[client->head].time);
client->buffer[client->head].type = type;
client->buffer[client->head].code = code;
client->buffer[client->head].value = value;
client->head = (client->head + 1) & (EVDEV_BUFFER_SIZE - 1);

kill_fasync(&client->fasync, SIGIO, POLL_IN);
} else
/* 遍厉client_list链表中的client结构(代表些打开evdev的进程(个人理解^_^)) */
list_for_each_entry(client, &evdev->client_list, node) {
/* 填充代表该输入信号的struct input_event结构(事件,类型,键码,键值) */
do_gettimeofday(&client->buffer[client->head].time);
client->buffer[client->head].type = type;
client->buffer[client->head].code = code;
client->buffer[client->head].value = value;
/* 更新写指针 */
client->head = (client->head + 1) & (EVDEV_BUFFER_SIZE - 1);

kill_fasync(&client->fasync, SIGIO, POLL_IN);//通知调用input_sync的进程:输入事件经已处理完毕(通知底层).
}

wake_up_interruptible(&evdev->wait);//唤醒睡眠在evdev->wait等待队列等待输入信息的进程(通知上层).
}

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好了,至此一个按键的输入事件处理完毕,现在再来从上到上的来看看用户是如何获取这个输入事件的.
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static const struct file_operations evdev_fops = {
.owner = THIS_MODULE,
.read = evdev_read,
.write = evdev_write,
.poll = evdev_poll,
.open = evdev_open,
.release = evdev_release,
.unlocked_ioctl = evdev_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = evdev_ioctl_compat,
#endif
.fasync = evdev_fasync,
.flush = evdev_flush
};


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

if (i >= EVDEV_MINORS)
return -ENODEV;

evdev = evdev_table[i];

if (!evdev || !evdev->exist)
return -ENODEV;

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

client->evdev = evdev;
/* 添加evdev_client结构到链表evdev->client_list中(好让输入事件到来的时候填写该结构并唤醒进程读取) */
list_add_tail(&client->node, &evdev->client_list);

if (!evdev->open++ && evdev->exist) {
error = input_open_device(&evdev->handle);
if (error) {
list_del(&client->node);
kfree(client);
return error;
}
}

file->private_data = client;//存放好evdev_client结构方便以后使用
return 0;
}


static ssize_t evdev_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
{
struct evdev_client *client = file->private_data;
struct evdev *evdev = client->evdev;
int retval;

if (count <>//对于每次读取的数据大小是有一定的要求.
return -EINVAL;

if (client->head == client->tail && evdev->exist && (file->f_flags & O_NONBLOCK))//缓存中没有数据可读且设备是存在的,
如果设置为NONBLOCK方式来读,立即返回.
return -EAGAIN;

retval = wait_event_interruptible(evdev->wait,
client->head != client->tail || !evdev->exist);//否则等待缓存有数据可读或设备不存在(被移去)
if (retval)
return retval;

if (!evdev->exist)
return -ENODEV;

while (client->head != client->tail && retval + evdev_event_size() <= count) {//下面开始读取数据

struct input_event *event = (struct input_event *) client->buffer + client->tail;//获取缓存中的读指针

if (evdev_event_to_user(buffer + retval, event))//返回数据给用户
return -EFAULT;

client->tail = (client->tail + 1) & (EVDEV_BUFFER_SIZE - 1);//更新读指针
retval += evdev_event_size();
}

return retval;
}

呵呵,看到了吧,应用程序就是这样获取输入事件的^_^

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本来对于gpio_keys这样的驱动程序,只要当发生按键事件的时候向上层应用程序汇报键值即可.
不过,对于一些带输出设备(例如led灯)的输入设备来说(例如键盘),上层应用程序同样可以利用event层来读取或改变其状态.
请看以下代码:
######################################################################################################################################

static ssize_t evdev_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos)
{
struct evdev_client *client = file->private_data;
struct evdev *evdev = client->evdev;
struct input_event event;
int retval = 0;

if (!evdev->exist)
return -ENODEV;

while (retval <>

if (evdev_event_from_user(buffer + retval, &event))//从用户处获取事件结构
return -EFAULT;
input_inject_event(&evdev->handle, event.type, event.code, event.value);//往底层发送事件
retval += evdev_event_size();
}

return retval;
}


/**
* input_inject_event() - send input event from input handler
* @handle: input handle to send event through
* @type: type of the event
* @code: event code
* @value: value of the event
*
* Similar to input_event() but will ignore event if device is "grabbed" and handle
* injecting event is not the one that owns the device.
*/
void input_inject_event(struct input_handle *handle, unsigned int type, unsigned int code, int value)
{
if (!handle->dev->grab || handle->dev->grab == handle)
input_event(handle->dev, type, code, value);
}
EXPORT_SYMBOL(input_inject_event);

/*
* input_event() - report new input event
* @dev: device that generated the event
* @type: type of the event
* @code: event code
* @value: value of the event
*
* This function should be used by drivers implementing various input devices
* See also input_inject_event()
*/
void input_event(struct input_dev *dev, unsigned int type, unsigned int code, int value)
{
struct input_handle *handle;

if (type > EV_MAX || !test_bit(type, dev->evbit))//首先判断该事件类型是否有效且为该设备所接受
return;

add_input_randomness(type, code, value);

switch (type) {

case EV_SYN:
switch (code) {
case SYN_CONFIG:
if (dev->event)
dev->event(dev, type, code, value);
break;

case SYN_REPORT:
if (dev->sync)
return;
dev->sync = 1;
break;
}
break;

.............................................................
case EV_LED:

if (code > LED_MAX || !test_bit(code, dev->ledbit) || !!test_bit(code, dev->led) == value)
return;

change_bit(code, dev->led);

if (dev->event)
dev->event(dev, type, code, value);

break;


if (type != EV_SYN)
dev->sync = 0;

if (dev->grab)
dev->grab->handler->event(dev->grab, type, code, value);
else
/*
* 循环调用所有处理该设备的handle(event,mouse,ts,joy等),
* 如果有进程打开了这些handle(进行读写),则调用其对应的event接口向气汇报该输入事件.
*/
list_for_each_entry(handle, &dev->h_list, d_node)
if (handle->open)
handle->handler->event(handle, type, code, value);
}
EXPORT_SYMBOL(input_event);

注:
鉴于简单的gpio_keys驱动中没有注册自己的event接口,当然也没有对于LED灯的处理,而event层只是简单的向上层汇报输入事件(event层也不可能帮你处理你的led设备,对吧),所以这个通过输入子系统控制LED的部分暂时不去研究.
(输出设备LED灯不属于这个输入设备gpio_key的一部分.当然,如果你想通过这个gpio_keys设备来控制led灯的话,可以修改这个gpio_keys驱动,详细可参考driver/input/keyboard目录下的驱动)