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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:#####################################################################################################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 < pdata->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 < pdata->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.#########################################################################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).}###################################################################################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.###################################################################################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 < evdev_event_size())//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^_^######################################################################################################################################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 < count) { 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)来源：