废话不多说，直接进入主题。在驱动insmod后，我们应用层对input设备如何操作？以下以全志a64为实例。
在/dev/input/eventX下(X的形成为后续会分析),是内核把接口暴露给应用层，一切操作都在这个文件上。
input子系统有两大部分，分别是input_dev和input_handler组成。
这两个的关系与device和driver类似，不同的是device只能对应一个driver，driver可以对应多个devcie，而handler可以对应多个device，device同样可以对应多个handler。
在linux-3.10/include/linux/input.h：
struct input_dev和struct input_handler都包含struct list_head h_list和struct list_head node。
node：device(driver)列表，一旦内核注册了一个input(hander)设备会加入device(driver)列表。
h_list：handl列表，一旦node匹配成功，会加入handle新的列表。
input和hander是通过struct list_head node这个纽带连接起来的，在input_dev中代表device，在input_handler中代表driver。
当input_dev和input_handler匹配成功后会初始化struct input_handle(注意这里不是er!)，这是input子系统的句柄，一切操作都通过handle。
input_handle包含struct list_head d_node和struct list_head h_node。
d_node：连接input_dev的h_list。
h_node：连接input_handler的h_list。
input_handle会记录input_dev和input_handler相关信息。
d_node
input_dev----------node |
| |
|<------------->input_handle
| |
input_handler-----node |
_node
大概流程知道了，就从代码分析吧！
这里从input子系统的注册开始，代码在linux-3.10/drivers/input/input.c除了初始化函数，还有其他函数，后续分析会调用到。
以下忽略初始化部分冗余代码：
1 static char *input_devnode(struct device *dev, umode_t *mode)
2 {
3 return kasprintf(GFP_KERNEL, "input/%s", dev_name(dev));
4 }
5
6 struct class input_class = {
7 .name = "input",
8 .devnode = input_devnode,
9 };
10 static int __init input_proc_init(void)
11 {
12 struct proc_dir_entry *entry;
13
14 proc_bus_input_dir = proc_mkdir("bus/input", NULL);
15
16 //input_devices_fileops会调用seq_operations
17 entry = proc_create("devices", 0, proc_bus_input_dir,
18 &input_devices_fileops);
19
20 entry = proc_create("handlers", 0, proc_bus_input_dir,
21 &input_handlers_fileops);
22
23 return 0;
24 }
25
26 static int __init input_init(void)
27 {
28 int err;
29
30 err = class_register(&input_class);
31
32 err = input_proc_init();
33
34 err = register_chrdev_region(MKDEV(INPUT_MAJOR, 0), //#define INPUT_MAJOR 13
35 INPUT_MAX_CHAR_DEVICES, "input"); //#define INPUT_MAX_CHAR_DEVICES 1024
36
37 return 0;
38 }
39
40 subsys_initcall(input_init);
41 module_exit(input_exit);从初始化的代码看，input_init只干了3件事情。
1：注册input class；
2：在/proc/bus/input创建devices和handlers属性，具体input_devices_fileops不分析，感兴趣可以cat里面的内容分析源码。
3：注册input字符设备。
input子系统初始化后继续分析，先从input_dev这部分看，以下以本人在全志a64平台上写的"my_key"为实例，my_key.c代码如下：
1 #include <linux/io.h>
2 #include <linux/gpio.h>
3 #include <linux/interrupt.h>
4 #include <linux/module.h>
5 #include <linux/of.h>
6 #include <linux/of_platform.h>
7 #include <linux/of_address.h>
8 #include <linux/of_device.h>
9 #include <linux/of_gpio.h>
10 #include <linux/pinctrl/consumer.h>
11 #include <linux/platform_device.h>
12 #include <linux/slab.h>
13 #include <linux/sys_config.h>
14 #include <linux/string.h>
15 #include <linux/delay.h>
16 #include <linux/input.h>
17 #include <linux/spinlock.h>
18
19 #define DEBUG
20 #ifdef DEBUG
21 #define dprintk(fmt, arg...) printk(KERN_DEBUG fmt, ##arg)
22 #else
23 #define dprintk(fmt, arg...)
24 #endif
25
26 static struct of_device_id mykey_of_match[] = {
27 { .compatible = "allwinner,mykey"},
28 };
29
30
31 struct key_dev {
32 struct pinctrl *pin;
33 int gpio;
34 int irq;
35 spinlock_t irq_lock;
36 struct work_struct work;
37 struct input_dev *input_dev;
38 };
39
40 static void handle_mykey(struct work_struct *work)
41 {
42 int val;
43 unsigned long irqflags;
44 struct key_dev *p_key = container_of(work, struct key_dev, work);
45
46 val = __gpio_get_value(p_key->gpio);
47
48 msleep(50);
49 if (val == __gpio_get_value(p_key->gpio)) {
50 dprintk("The key val is %d.\n", val);
51 if (val)
52 input_report_key(p_key->input_dev, KEY_ENTER, 1); //松开
53 else
54 input_report_key(p_key->input_dev, KEY_ENTER, 0); //按下
55 input_sync(p_key->input_dev);
56 }
57
58 spin_lock_irqsave(&p_key->irq_lock, irqflags);
59 enable_irq(p_key->irq);
60 spin_unlock_irqrestore(&p_key->irq_lock, irqflags);
61
62 }
63
64 static irqreturn_t mykey_irq_handler(int irq, void *dev_id)
65 {
66 struct key_dev *p_key = dev_id;
67 unsigned long irqflags;
68
69 spin_lock_irqsave(&p_key->irq_lock, irqflags);
70 disable_irq_nosync(p_key->irq);
71 spin_unlock_irqrestore(&p_key->irq_lock, irqflags);
72
73 dprintk("in interrupt\n");
74 schedule_work(&p_key->work); //工作队列中断下半部分
75 return IRQ_HANDLED;
76 }
77
78 static int mykey_probe(struct platform_device *pdev)
79 {
80 struct device_node *node = pdev->dev.of_node;
81 struct key_dev *p_key;
82
83 int ret;
84 dprintk("Initializing my_key.\n");
85
86 p_key = devm_kzalloc(&pdev->dev, sizeof(*p_key), GFP_KERNEL);
87 if (IS_ERR(p_key)) {
88 printk(KERN_ERR "Failed to kzalloc p_key.\n");
89 ret = -1;
90 goto out;
91 }
92
93 p_key->pin = devm_pinctrl_get_select(&pdev->dev, "default"); //初始化IO口状态配置
94 if (IS_ERR(p_key->pin)) {
95 printk(KERN_ERR "Failed to get_select pin.\n");
96 ret = -1;
97 goto out;
98 }
99
100 p_key->gpio = of_get_named_gpio(node, "mykey-gpio", 0); //从设备树得到IO句柄
101
102 ret = devm_gpio_request(&pdev->dev, p_key->gpio, NULL);
103 if (ret) {
104 printk(KERN_ERR "Failed to request gpio:%d.\n", p_key->gpio);
105 goto out;
106 }
107
108 //获取gpio对应的irq号并申请中断
109 p_key->irq = gpio_to_irq(p_key->gpio);
110 ret = devm_request_irq(&pdev->dev, p_key->irq, mykey_irq_handler, IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING, "MYKEY_EINT", (void *)p_key);
111 if (ret) {
112 printk(KERN_ERR "Failed to request irq: %d.\n", p_key->irq);
113 goto out;
114 }
115
116 p_key->input_dev = devm_input_allocate_device(&pdev->dev); //开启资源回收 & 分配input_dev结构空间并初始化h_list和node
117 if (IS_ERR(p_key->input_dev)) {
118 printk(KERN_ERR "Failed to allocate input device.\n");
119 ret = -1;
120 goto out;
121 }
122
123 p_key->input_dev->name = "my_key";
124 p_key->input_dev->evbit[0] = BIT_MASK(EV_KEY); //设置KEY事件
125 set_bit(KEY_ENTER, p_key->input_dev->keybit); //key事件对应具体操作码
126 set_bit(KEY_ENTER, p_key->input_dev->key); //把key事件对应具体操作码的状态置1(电路常态是高电平)
127 ret = input_register_device(p_key->input_dev);
128 if (ret) {
129 printk(KERN_ERR "Failed to register input_device.\n");
130 goto out;
131 }
132 INIT_WORK (&p_key->work, handle_mykey); //初始化队列
133 spin_lock_init(&p_key->irq_lock);
134
135 platform_set_drvdata(pdev, p_key);
136 return 0;
137 out:
138 return ret;
139 }
140
141 static int mykey_remove(struct platform_device *pdev)
142 {
143 struct key_dev *p_key = platform_get_drvdata(pdev);
144 flush_work(&p_key->work);
145 return 0;
146 }
147
148 static struct platform_driver mykey_driver = {
149 .probe = mykey_probe,
150 .remove = mykey_remove,
151 .driver = {
152 .name = "mykey",
153 .owner = THIS_MODULE,
154 .of_match_table = of_match_ptr(mykey_of_match),
155 },
156 };
157 module_platform_driver(mykey_driver);
158
159 MODULE_AUTHOR("Kevin Hwang <kevin.hwang@live.com");
160 MODULE_LICENSE("GPL v2");注释已经很明白，重点分析input_register_device，在linux-3.10/drivers/input/input.c定义。
忽略部分代码如下：
1 int input_register_device(struct input_dev *dev)
2 {
3 static atomic_t input_no = ATOMIC_INIT(0);
4 struct input_devres *devres = NULL;
5 struct input_handler *handler;
6 unsigned int packet_size;
7 const char *path;
8 int error;
9
10 if (dev->devres_managed) {
11 devres = devres_alloc(devm_input_device_unregister,
12 sizeof(struct input_devres), GFP_KERNEL);
13 devres->input = dev;
14 }
15
16 /* Every input device generates EV_SYN/SYN_REPORT events. */
17 __set_bit(EV_SYN, dev->evbit);
18
19 /* KEY_RESERVED is not supposed to be transmitted to userspace. */
20 __clear_bit(KEY_RESERVED, dev->keybit);
21
22 /* Make sure that bitmasks not mentioned in dev->evbit are clean. */
23 input_cleanse_bitmasks(dev);
24
25 packet_size = input_estimate_events_per_packet(dev); //估算input_dev上报数据需要多少缓存空间，这里pack_size=8
26 if (dev->hint_events_per_packet < packet_size)
27 dev->hint_events_per_packet = packet_size;
28
29 dev->max_vals = max(dev->hint_events_per_packet, packet_size) + 2; //对于my_key，max_vals=10
30 dev->vals = kcalloc(dev->max_vals, sizeof(*dev->vals), GFP_KERNEL);
31
32 /*
33 * If delay and period are pre-set by the driver, then autorepeating
34 * is handled by the driver itself and we don't do it in input.c.
35 */
36 init_timer(&dev->timer);
37 if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD]) {
38 dev->timer.data = (long) dev;
39 dev->timer.function = input_repeat_key;
40 dev->rep[REP_DELAY] = 250;
41 dev->rep[REP_PERIOD] = 33;
42 }
43
44 if (!dev->getkeycode)
45 dev->getkeycode = input_default_getkeycode;
46
47 if (!dev->setkeycode)
48 dev->setkeycode = input_default_setkeycode;
49
50 dev_set_name(&dev->dev, "input%ld",
51 (unsigned long) atomic_inc_return(&input_no) - 1);
52
53 error = device_add(&dev->dev);
54
55 path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
56 pr_info("%s as %s\n",
57 dev->name ? dev->name : "Unspecified device",
58 path ? path : "N/A");
59 kfree(path);
60
61 list_add_tail(&dev->node, &input_dev_list); //把input_dev的node成员插入到全局input_dev_list
62
63 list_for_each_entry(handler, &input_handler_list, node) //input_dev和input_handler匹配
64 input_attach_handler(dev, handler);
65
66
67 if (dev->devres_managed) {
68 dev_dbg(dev->dev.parent, "%s: registering %s with devres.\n",
69 __func__, dev_name(&dev->dev));
70 devres_add(dev->dev.parent, devres);
71 }
72 return 0;
73 }input_attach_handler的实现后续再分析，现在input_dev(device)已经准备就绪，就差input_handler(driver)。
对应"my_key"的handler在linux3.10/drivers/input/evdev.c，初始化代码如下：
1 static const struct input_device_id evdev_ids[] = {
2 { .driver_info = 1 }, /* Matches all devices */
3 { }, /* Terminating zero entry */
4 };
5
6 MODULE_DEVICE_TABLE(input, evdev_ids);
7
8 static struct input_handler evdev_handler = {
9 .event = evdev_event,
10 .events = evdev_events,
11 .connect = evdev_connect,
12 .disconnect = evdev_disconnect,
13 .legacy_minors = true,
14 .minor = EVDEV_MINOR_BASE, //#define EVDEV_MINOR_BASE 64
15 .name = "evdev",
16 .id_table = evdev_ids,
17 };
18
19 static int __init evdev_init(void)
20 {
21 return input_register_handler(&evdev_handler);
22 }
23
24 static void __exit evdev_exit(void)
25 {
26 input_unregister_handler(&evdev_handler);
27 }
28
29 module_init(evdev_init);
30 module_exit(evdev_exit);对于evdev而言，他的次设备是从64开始的。evdev_init只调用了input_register_handler，在linux-3.10/drivers/input/input.c定义。
忽略部分代码：
1 int input_register_handler(struct input_handler *handler)
2 {
3 struct input_dev *dev;
4
5 INIT_LIST_HEAD(&handler->h_list); //初始化input_handler的h_list
6
7 list_add_tail(&handler->node, &input_handler_list); //把input_handler的node成员插入到全局input_handler_list
8
9 list_for_each_entry(dev, &input_dev_list, node)
10 input_attach_handler(dev, handler); //input_dev和input_handler匹配
11
12 return 0;
13 }这里又出现了input_attach_handler，现在input_dev和input_handler都有了，看看里面如何匹配。
1 static const struct input_device_id *input_match_device(struct input_handler *handler,
2 struct input_dev *dev)
3 {
4 const struct input_device_id *id;
5
6 for (id = handler->id_table; id->flags || id->driver_info; id++) {
7
8 if (id->flags & INPUT_DEVICE_ID_MATCH_BUS)
9 if (id->bustype != dev->id.bustype)
10 continue;
11
12 if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR)
13 if (id->vendor != dev->id.vendor)
14 continue;
15
16 if (id->flags & INPUT_DEVICE_ID_MATCH_PRODUCT)
17 if (id->product != dev->id.product)
18 continue;
19
20 if (id->flags & INPUT_DEVICE_ID_MATCH_VERSION)
21 if (id->version != dev->id.version)
22 continue;
23 //bitmap_subset：argv1是否是argv2子集，若真返回1，假返回0。argv3是要校验的位数
24 //这里evdev是空集(id->xxxbit都是0)，是所有input_dev的子集
25 if (!bitmap_subset(id->evbit, dev->evbit, EV_MAX))
26 continue;
27
28 if (!bitmap_subset(id->keybit, dev->keybit, KEY_MAX))
29 continue;
30
31 if (!bitmap_subset(id->relbit, dev->relbit, REL_MAX))
32 continue;
33
34 if (!bitmap_subset(id->absbit, dev->absbit, ABS_MAX))
35 continue;
36
37 if (!bitmap_subset(id->mscbit, dev->mscbit, MSC_MAX))
38 continue;
39
40 if (!bitmap_subset(id->ledbit, dev->ledbit, LED_MAX))
41 continue;
42
43 if (!bitmap_subset(id->sndbit, dev->sndbit, SND_MAX))
44 continue;
45
46 if (!bitmap_subset(id->ffbit, dev->ffbit, FF_MAX))
47 continue;
48
49 if (!bitmap_subset(id->swbit, dev->swbit, SW_MAX))
50 continue;
51
52 if (!handler->match || handler->match(handler, dev))
53 return id;
54 }
55
56 return NULL;
57 }
58
59 static int input_attach_handler(struct input_dev *dev, struct input_handler *handler)
60 {
61 const struct input_device_id *id;
62 int error;
63
64 id = input_match_device(handler, dev);
65 if (!id)
66 return -ENODEV;
67
68 error = handler->connect(handler, dev, id);
69 if (error && error != -ENODEV)
70 pr_err("failed to attach handler %s to device %s, error: %d\n",
71 handler->name, kobject_name(&dev->dev.kobj), error);
72
73 return error;
74 }input_attach_handler做了两件事情，匹配和连接相应handler，因evdev_ids匹配所有input_device，所以这里就直接调用handler->connect = evdev_connect。
看看evdev_connect做了什么事情，回到linux3.10/drivers/input/evdev.c，
忽略部分冗余代码，并加上部分源码注释：
1 static const struct file_operations evdev_fops = {
2 .owner = THIS_MODULE,
3 .read = evdev_read,
4 .write = evdev_write,
5 .poll = evdev_poll,
6 .open = evdev_open,
7 .release = evdev_release,
8 .unlocked_ioctl = evdev_ioctl,
9 #ifdef CONFIG_COMPAT
10 .compat_ioctl = evdev_ioctl_compat,
11 #endif
12 .fasync = evdev_fasync,
13 .flush = evdev_flush,
14 .llseek = no_llseek,
15 };
16
17 static int evdev_connect(struct input_handler *handler, struct input_dev *dev,
18 const struct input_device_id *id)
19 {
20 struct evdev *evdev;
21 int minor;
22 int dev_no;
23 int error;
24 //生成64~64+32的次设备号
25 minor = input_get_new_minor(EVDEV_MINOR_BASE, EVDEV_MINORS, true);
26
27 evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);
28
29 INIT_LIST_HEAD(&evdev->client_list);
30 spin_lock_init(&evdev->client_lock);
31 mutex_init(&evdev->mutex);
32 init_waitqueue_head(&evdev->wait);
33 evdev->exist = true;
34
35 dev_no = minor;
36 /* Normalize device number if it falls into legacy range */
37 if (dev_no < EVDEV_MINOR_BASE + EVDEV_MINORS)
38 dev_no -= EVDEV_MINOR_BASE; //次设备号减去偏移
39 dev_set_name(&evdev->dev, "event%d", dev_no);
40
41 //初始化handle
42 evdev->handle.dev = input_get_device(dev);
43 evdev->handle.name = dev_name(&evdev->dev);
44 evdev->handle.handler = handler;
45 evdev->handle.private = evdev;
46
47 //初始化device
48 evdev->dev.devt = MKDEV(INPUT_MAJOR, minor);
49 evdev->dev.class = &input_class;
50 evdev->dev.parent = &dev->dev;
51 evdev->dev.release = evdev_free;
52 device_initialize(&evdev->dev);
53
54 error = input_register_handle(&evdev->handle);
55
56 // int input_register_handle(struct input_handle *handle)
57 // {
58 // struct input_handler *handler = handle->handler;
59 // struct input_dev *dev = handle->dev;
60
61 // list_add_tail_rcu(&handle->d_node, &dev->h_list); 把input_handle的d_node加入input_dev的h_list
62
63 // list_add_tail_rcu(&handle->h_node, &handler->h_list); 把input_handle的h_node加入input_handler的h_list
64
65 // return 0;
66 // }
67
68 // 初始化并注册字符设备
69 cdev_init(&evdev->cdev, &evdev_fops);
70 evdev->cdev.kobj.parent = &evdev->dev.kobj;
71 error = cdev_add(&evdev->cdev, evdev->dev.devt, 1);
72
73 error = device_add(&evdev->dev);
74
75 return 0;
76 }比较有趣的evdev_connect并没有用到argv3的struct input_device_id *id，因为evdev这个handler是可以匹配全部device的。
现在handle已经连接好dev和handler并且注册eventX，对eventX的操作都在evdev_fops。
在应用层open&read eventX，eventX到底是如何上报数据的?
由以上分析得到evdev_fops.open = evdev_open。
忽略部分冗余代码，并加上部分源码注释：
1 static int evdev_open(struct inode *inode, struct file *file)
2 {
3 struct evdev *evdev = container_of(inode->i_cdev, struct evdev, cdev);
4 unsigned int bufsize = evdev_compute_buffer_size(evdev->handle.dev); //bufsize=64
5 // static unsigned int evdev_compute_buffer_size(struct input_dev *dev) 函数定义
6 // {
7 // unsigned int n_events =
8 // max(dev->hint_events_per_packet * EVDEV_BUF_PACKETS, #define EVDEV_BUF_PACKETS 8
9 // EVDEV_MIN_BUFFER_SIZE);
10
11 // return roundup_pow_of_two(n_events); 8*8=64刚好是2^6
12 // }
13 unsigned int size = sizeof(struct evdev_client) +
14 bufsize * sizeof(struct input_event);
15 struct evdev_client *client;
16 int error;
17
18 client = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
19
20 client->bufsize = bufsize;
21 spin_lock_init(&client->buffer_lock);
22 snprintf(client->name, sizeof(client->name), "%s-%d",
23 dev_name(&evdev->dev), task_tgid_vnr(current));
24 client->evdev = evdev;
25 evdev_attach_client(evdev, client); //把client的node插入到evdev的client_list
26
27 // static void evdev_attach_client(struct evdev *evdev, struct evdev_client *client) 函数定义
28 // {
29 // spin_lock(&evdev->client_lock);
30 // list_add_tail_rcu(&client->node, &evdev->client_list);
31 // spin_unlock(&evdev->client_lock);
32 // }
33
34 error = evdev_open_device(evdev);
35 // static int evdev_open_device(struct evdev *evdev) 函数定义
36 // {
37 // int retval;
38 // if (!evdev->exist)
39 // retval = -ENODEV;
40 // else if (!evdev->open++) { 第一次open才调用input_open_device
41 // retval = input_open_device(&evdev->handle);
42 // }
43 // return retval;
44 //}
45 file->private_data = client; //以后操作文件都通过client
46 return 0;
47 }注释已经很清晰，如果第一次调用open，需要调用input_open_device，在linux-3.10/drivers/input/input.c定义。
忽略部分冗余代码：
1 int input_open_device(struct input_handle *handle)
2 {
3 struct input_dev *dev = handle->dev;
4 int retval;
5
6 handle->open++;
7
8 if (!dev->users++ && dev->open) //"my_key"的dev->open = NULL，不执行dev->open(dev)
9 retval = dev->open(dev);
10
11 return retval;
12 }在"my_key"的实例中，input_open_device只干了一件有意义的事情就是handle->open++，到这里open的操作很清晰，主要是初始化client，因为后续的read都是在client操作的。
既然已经open成功了，后面看看evdev_read做了什么。
忽略部分冗余代码，并加上部分源码注释：
1 static ssize_t evdev_read(struct file *file, char __user *buffer,
2 size_t count, loff_t *ppos)
3 {
4 struct evdev_client *client = file->private_data;
5 struct evdev *evdev = client->evdev;
6 struct input_event event;
7 size_t read = 0;
8 int error;
9
10 for (;;) {
11 if (!evdev->exist)
12 return -ENODEV;
13
14 if (client->packet_head == client->tail &&
15 (file->f_flags & O_NONBLOCK))
16 return -EAGAIN;
17
18 while (read + input_event_size() <= count &&
19 evdev_fetch_next_event(client, &event)) { //evdev_fetch_next_event到bufsize次就会逻辑假
20 // static int evdev_fetch_next_event(struct evdev_client *client, struct input_event *event) 函数定义
21 // {
22 // int have_event;
23 // 通过client->tail &= client->bufsize - 1会使client->packet_head == client->tail
24 // have_event = client->packet_head != client->tail;
25 // if (have_event) {
26 // *event = client->buffer[client->tail++];
27 // client->tail &= client->bufsize - 1;
28 // }
29 // return have_event;
30 // }
31
32 if (input_event_to_user(buffer + read, &event)) //copy_to_user多了一层壳而已
33 return -EFAULT;
34 // int input_event_to_user(char __user *buffer, const struct input_event *event) 函数定义
35 // {
36 // if (copy_to_user(buffer, event, sizeof(struct input_event)))
37 // return -EFAULT;
38 // }
39 read += input_event_size();
40 }
41
42 if (read) //如果读到数据
43 break;
44
45 if (!(file->f_flags & O_NONBLOCK)) { //如果阻塞
46 error = wait_event_interruptible(evdev->wait, //唤醒判断client有无数据或者evdev release
47 client->packet_head != client->tail ||
48 !evdev->exist);
49 if (error)
50 return error;
51 }
52 }
53
54 return read;
55 }
添加了注释不能理解，这里有两个疑问。
1：什么函数使client->packet_head != client->tail并填充client->buffer?
2：若读阻塞，什么函数唤醒队列?
回到my_key.c，当按键触发中断的时候，会调用：
松开input_report_key(input_mykey_dev, KEY_ENTER, 1);input_sync(input_mykey_dev)；
按下input_report_key(input_mykey_dev, KEY_ENTER, 0);input_sync(input_mykey_dev)；
input_report_key和input_sync均在linux-3.10/drivers/input/input.c定义。
1 static inline void input_report_key(struct input_dev *dev, unsigned int code, int value)
2 {
3 input_event(dev, EV_KEY, code, !!value);
4 }
5
6 static inline void input_sync(struct input_dev *dev)
7 {
8 input_event(dev, EV_SYN, SYN_REPORT, 0);
9 }可见最终还是调用input_event，其在linux-3.10/drivers/input/input.c定义。
忽略部分冗余代码，并加上部分源码注释：
1 void input_event(struct input_dev *dev,
2 unsigned int type, unsigned int code, int value)
3 {
4 unsigned long flags;
5
6 if (is_event_supported(type, dev->evbit, EV_MAX)) {
7 input_handle_event(dev, type, code, value);
8 // static void input_handle_event(struct input_dev *dev,
9 // unsigned int type, unsigned int code, int value) 函数定义
10 // {
11 // int disposition;
12
13 // disposition = input_get_disposition(dev, type, code, &value);
14 // // static int input_get_disposition(struct input_dev *dev, unsigned int type, unsigned int code, int *pval) 函数定义
15 // // {
16 // // int disposition = INPUT_IGNORE_EVENT;
17 // // int value = *pval;
18
19 // // switch (type) {
20
21 // // case EV_SYN:
22 // // switch (code) {
23 // // case SYN_CONFIG:
24 // // disposition = INPUT_PASS_TO_ALL;
25 // // break;
26
27 // // case SYN_REPORT: "my_key"调用input_event(dev, EV_SYN, SYN_REPORT, 0);
28 // // disposition = INPUT_PASS_TO_HANDLERS | INPUT_FLUSH;
29 // // break;
30 // // case SYN_MT_REPORT:
31 // // disposition = INPUT_PASS_TO_HANDLERS;
32 // // break;
33 // // }
34 // // break;
35
36 // // case EV_KEY: "my_key"调用input_event(dev, EV_KEY, code, !!value);
37 // // if (is_event_supported(code, dev->keybit, KEY_MAX)) {
38
39 // // /* auto-repeat bypasses state updates */
40 // // if (value == 2) {
41 // // disposition = INPUT_PASS_TO_HANDLERS;
42 // // break;
43 // // }
44
45 // // if (!!test_bit(code, dev->key) != !!value) { 若dev->key对应code的状态(0/1)和value不同则执行
46 // // __change_bit(code, dev->key); 反向dev->key对应code的状态
47 // // disposition = INPUT_PASS_TO_HANDLERS;
48 // // }
49 // // }
50 // // break;
51 // // case EV_SW: ...... 这里分析忽略不相关的type
52 // // case EV_ABS: ......
53 // // case EV_REL: ......
54 // // case EV_MSC: ......
55 // // case EV_LED: ......
56 // // case EV_SND: ......
57 // // case EV_REP: ......
58 // // case EV_FF: ......
59 // // case EV_PWR: ......
60 // // }
61 // // *pval = value;
62 // // return disposition;
63 // // }
64
65 // if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event)
66 // dev->event(dev, type, code, value);
67
68 // if (disposition & INPUT_PASS_TO_HANDLERS) { input_event(dev, EV_KEY, code, !!value)和input_event(dev, EV_SYN, SYN_REPORT, 0)
69 // struct input_value *v; 下disposition都有INPUT_PASS_TO_HANDLERS状态，执行两次
70
71 // if (disposition & INPUT_SLOT) {
72 // v = &dev->vals[dev->num_vals++];
73 // v->type = EV_ABS;
74 // v->code = ABS_MT_SLOT;
75 // v->value = dev->mt->slot;
76 // }
77
78 // v = &dev->vals[dev->num_vals++]; //调用input_event(dev, EV_SYN, SYN_REPORT, 0)后，dev->num_vals=2
79 // v->type = type;
80 // v->code = code;
81 // v->value = value;
82 // }
83
84 // if (disposition & INPUT_FLUSH) { input_event(dev, EV_SYN, SYN_REPORT, 0)，disposition有INPUT_FLUSH状态
85 // if (dev->num_vals >= 2)
86 // input_pass_values(dev, dev->vals, dev->num_vals);
87 // // static void input_pass_values(struct input_dev *dev, struct input_value *vals, unsigned int count) 函数定义
88 // // {
89 // // struct input_handle *handle;
90 // // struct input_value *v;
91
92 // // handle = rcu_dereference(dev->grab); 这里dev->grab=0，可以通过EVIOCGRAB ioctl改变
93 // // if (handle) {
94 // // count = input_to_handler(handle, vals, count);
95 // // } else {
96 // // list_for_each_entry_rcu(handle, &dev->h_list, d_node) 通过dev->h_list找到handle
97 // // if (handle->open)
98 // // count = input_to_handler(handle, vals, count);
99 // // //static unsigned int input_to_handler(struct input_handle *handle, 函数定义
100 // // // struct input_value *vals, unsigned int count)
101 // // //{
102 // // // struct input_handler *handler = handle->handler;
103 // // // struct input_value *end = vals;
104 // // // struct input_value *v;
105
106 // // // for (v = vals; v != vals + count; v++) {
107 // // // if (handler->filter && evdev的handler->filte=NULL
108 // // // handler->filter(handle, v->type, v->code, v->value))
109 // // // continue;
110 // // // if (end != v)
111 // // // *end = *v;
112 // // // end++;
113 // // // }
114
115 // // // count = end - vals; 这里count=2
116
117 // // // if (handler->events) 直接调用evdev_handler.events=evdev_events
118 // // // handler->events(handle, vals, count);
119 // // // else if (handler->event)
120 // // // for (v = vals; v != end; v++)
121 // // // handler->event(handle, v->type, v->code, v->value);
122
123 // // // return count;
124 // // //}
125 // // }
126 // // /* trigger auto repeat for key events */
127 // // for (v = vals; v != vals + count; v++) {
128 // // if (v->type == EV_KEY && v->value != 2) { 能进来这里v->type=EV_SYN，故不执行
129 // // if (v->value)
130 // // input_start_autorepeat(dev, v->code);
131 // // else
132 // // input_stop_autorepeat(dev);
133 // // }
134 // // }
135 // // }
136 // dev->num_vals = 0;
137 // } else if (dev->num_vals >= dev->max_vals - 2) {
138 // dev->vals[dev->num_vals++] = input_value_sync;
139 // input_pass_values(dev, dev->vals, dev->num_vals);
140 // dev->num_vals = 0;
141 // }
142
143 // }
144 }
145 }从以上源码可以得知，单一调用input_report_key(input_mykey_dev, KEY_ENTER, 0/1)，无法上报，因为没有EV_SYN刷新。
除了evdev_events的源码没分析外，我们仍然不能解决我们上面提的两个问题，那么解决那两个问题肯定是在evdev_events里面。
evdev_events在linux3.10/drivers/input/evdev.c定义。
忽略部分冗余代码，并加上部分源码注释：
1 static void evdev_events(struct input_handle *handle,
2 const struct input_value *vals, unsigned int count)
3 {
4 struct evdev *evdev = handle->private;
5 struct evdev_client *client;
6 ktime_t time_mono, time_real;
7
8 time_mono = ktime_get();
9 time_real = ktime_sub(time_mono, ktime_get_monotonic_offset());
10
11
12 client = rcu_dereference(evdev->grab); //这里evdev->grab=0，可以通过EVIOCGRAB ioctl改变
13
14 if (client)
15 evdev_pass_values(client, vals, count, time_mono, time_real);
16 else
17 list_for_each_entry_rcu(client, &evdev->client_list, node)
18 evdev_pass_values(client, vals, count, time_mono, time_real);
19 //static void evdev_pass_values(struct evdev_client *client, const struct input_value *vals, unsigned int count,
20 // ktime_t mono, ktime_t real) 函数定义
21 //{
22 // struct evdev *evdev = client->evdev;
23 // const struct input_value *v;
24 // struct input_event event;
25 // bool wakeup = false;
26
27 // event.time = ktime_to_timeval（client->clkid == CLOCK_MONOTONIC ? mono : real);
28
29 // for (v = vals; v != vals + count; v++) {
30 // event.type = v->type;
31 // event.code = v->code;
32 // event.value = v->value;
33 // __pass_event(client, &event);
34 // static void __pass_event(struct evdev_client *client, const struct input_event *event)
35 // {
36 // client->buffer[client->head++] = *event; 这里head比tail领先
37 // client->head &= client->bufsize - 1;
38
39 // if (unlikely(client->head == client->tail)) { 太久没同步client->head饶了一圈
40 // /*
41 // * This effectively "drops" all unconsumed events, leaving
42 // * EV_SYN/SYN_DROPPED plus the newest event in the queue.
43 // */
44 // client->tail = (client->head - 2) & (client->bufsize - 1);
45
46 // client->buffer[client->tail].time = event->time;
47 // client->buffer[client->tail].type = EV_SYN;
48 // client->buffer[client->tail].code = SYN_DROPPED;
49 // client->buffer[client->tail].value = 0;
50
51 // client->packet_head = client->tail;
52 // }
53
54 // if (event->type == EV_SYN && event->code == SYN_REPORT) {
55 // client->packet_head = client->head; 问题1：改变packet_head
56 // kill_fasync(&client->fasync, SIGIO, POLL_IN); 异步通知应用
57 // }
58 // }
59 // if (v->type == EV_SYN && v->code == SYN_REPORT)
60 // wakeup = true;
61 // }
62 //
63 // if (wakeup)
64 // wake_up_interruptible(&evdev->wait); 问题2：在这里唤醒
65 //}
66
67 }解决以上两个问题都在__pass_event，对于第一个问题这里需要注意的是client->packet_head领先于client->tail，client->tail追赶client->packet_head。
总结上报过程(前提已经打开设备，这样才会生成client)：input_report_key--->input_event--->input_handle_event--->等待input_sync执行
input_sync--->input_event--->input_handle_event--->input_pass_values--->input_to_handler--->evdev_events--->__pass_event在控制台执行busybox hexdump /dev/input/event5 (X=5)
[ 3915.739133] in interrupt
[ 3915.792895] The key val is 0.
00000c0 c772 57bd c3f6 000d 0001 001c 0000 0000
00000d0 c772 57bd c3f6 000d 0000 0000 0000 0000
[ 3915.860499] in interrupt
[ 3915.920814] The key val is 1.
00000e0 c773 57bd 7d86 0000 0001 001c 0001 0000
00000f0 c773 57bd 7d86 0000 0000 0000 0000 0000
注意，这里是小端
0x57bdc772 是秒，0x000dc3f6是毫秒，0x0001是type=EV_KEY，0x001c是code=KEY_ENTER，0x00000001是value
到此input子系统的按键例子已经分析完~
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