input子系统框架
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。
/----------h_list<-------------->d_node
input_dev----------node |
| |
|<------------->input_handle
| |
input_handler-----node |
\----------h_list<------------>h_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~
