/**
 * input_allocate_device - allocate memory for new input device
 *
 * Returns prepared struct input_dev or NULL.
 *
 * NOTE: Use input_free_device() to free devices that have not been
 * registered; input_unregister_device() should be used for already
 * registered devices.
 */
struct input_dev *input_allocate_device(void)
{
    struct input_dev *dev;
         /*分配一个input_dev结构体，并初始化为0*/ 
    dev = kzalloc(sizeof(struct input_dev), GFP_KERNEL);
    if (dev) {
        dev->dev.type = &input_dev_type;/*初始化设备的类型*/  
        dev->dev.class = &input_class; /*设置为输入设备类*/  
        device_initialize(&dev->dev);/*初始化device结构*/ 
        mutex_init(&dev->mutex); /*初始化互斥锁*/ 
        spin_lock_init(&dev->event_lock); /*初始化事件自旋锁*/  
        INIT_LIST_HEAD(&dev->h_list);/*初始化链表*/ 
        INIT_LIST_HEAD(&dev->node); /*初始化链表*/  

        __module_get(THIS_MODULE);/*模块引用技术加1*/  
    }

    return dev;
}    

/**
 * input_register_device - register device with input core
 * @dev: device to be registered
 *
 * This function registers device with input core. The device must be
 * allocated with input_allocate_device() and all it''s capabilities
 * set up before registering.
 * If function fails the device must be freed with input_free_device().
 * Once device has been successfully registered it can be unregistered
 * with input_unregister_device(); input_free_device() should not be
 * called in this case.
 */
int input_register_device(struct input_dev *dev)
{
       //定义一些函数中将用到的局部变量
    static atomic_t input_no = ATOMIC_INIT(0);
    struct input_handler *handler;
    const char *path;
    int error;
    //设置 input_dev 所支持的事件类型，由 evbit 成员来表示。具体类型在后面归纳。
    /* 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);

     //初始化 timer 定时器，用来处理重复点击按键。(去抖)
    /*
     * 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.
     */
    init_timer(&dev->timer);
       //如果 rep[REP_DELAY] 和 [REP_PERIOD] 没有设值，则赋默认值。为了去抖。
    if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD]) {
        dev->timer.data = (long) dev;
        dev->timer.function = input_repeat_key;
        dev->rep[REP_DELAY] = 250;
        dev->rep[REP_PERIOD] = 33;
    }
     //检查下列两个函数是否被定义，没有被定义则赋默认值。
    if (!dev->getkeycode)
        dev->getkeycode = input_default_getkeycode;//得到指定位置键值

    if (!dev->setkeycode)
        dev->setkeycode = input_default_setkeycode;//设置指定位置键值
       //设置 input_dev 中 device 的名字为 inputN
       //将如 input0 input1 input2 出现在 sysfs 文件系统中
    dev_set_name(&dev->dev, "input%ld",
             (unsigned long) atomic_inc_return(&input_no) - 1);
       //将 input->dev 包含的 device 结构注册到 Linux 设备模型中。
    error = device_add(&dev->dev);
    if (error)
        return error;
    //打印设备的路径并输出调试信息
    path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
    printk(KERN_INFO "input: %s as %s\n",
        dev->name ? dev->name : "Unspecified device", path ? path : "N/A");
    kfree(path);

    error = mutex_lock_interruptible(&input_mutex);
    if (error) {
        device_del(&dev->dev);
        return error;
    }
       //将 input_dev 加入 input_dev_list 链表中（这个链表中包含有所有 input 设备）
    list_add_tail(&dev->node, &input_dev_list);

    list_for_each_entry(handler, &input_handler_list, node)
      //调用 input_attatch_handler()函数匹配 handler 和 input_dev。
       //这个函数很重要，在后面单独分析。
        input_attach_handler(dev, handler);

    input_wakeup_procfs_readers();

    mutex_unlock(&input_mutex);

    return 0;
}

struct input_handle;

/**
 * struct input_handler - implements one of interfaces for input devices
 * @private: driver-specific data
 * @event: event handler. This method is being called by input core with
 *    interrupts disabled and dev->event_lock spinlock held and so
 *    it may not sleep
 * @filter: similar to @event; separates normal event handlers from
 *    "filters".
 * @match: called after comparing device''s id with handler''s id_table
 *    to perform fine-grained matching between device and handler
 * @connect: called when attaching a handler to an input device
 * @disconnect: disconnects a handler from input device
 * @start: starts handler for given handle. This function is called by
 *    input core right after connect() method and also when a process
 *    that "grabbed" a device releases it
 * @fops: file operations this driver implements
 * @minor: beginning of range of 32 minors for devices this driver
 *    can provide
 * @name: name of the handler, to be shown in /proc/bus/input/handlers
 * @id_table: pointer to a table of input_device_ids this driver can
 *    handle
 * @h_list: list of input handles associated with the handler
 * @node: for placing the driver onto input_handler_list
 *
 * Input handlers attach to input devices and create input handles. There
 * are likely several handlers attached to any given input device at the
 * same time. All of them will get their copy of input event generated by
 * the device.
 *
 * The very same structure is used to implement input filters. Input core
 * allows filters to run first and will not pass event to regular handlers
 * if any of the filters indicate that the event should be filtered (by
 * returning %true from their filter() method).
 *
 * Note that input core serializes calls to connect() and disconnect()
 * methods.
 */
struct input_handler {

    void *private;

    void (*event)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
    bool (*filter)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
    bool (*match)(struct input_handler *handler, struct input_dev *dev);
    int (*connect)(struct input_handler *handler, struct input_dev *dev, const struct input_device_id *id);
    void (*disconnect)(struct input_handle *handle);
    void (*start)(struct input_handle *handle);

    const struct file_operations *fops;
    int minor;
    const char *name;

    const struct input_device_id *id_table;

    struct list_head    h_list;
    struct list_head    node;
};

Programming input drivers
~~~~~~~~~~~~~~~~~~~~~~~~~

1. Creating an input device driver
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1.0 The simplest example
~~~~~~~~~~~~~~~~~~~~~~~~

Here comes a very simple example of an input device driver. The device has
just one button and the button is accessible at i/o port BUTTON_PORT. When
pressed or released a BUTTON_IRQ happens. The driver could look like:

#include <linux/input.h>
#include <linux/module.h>
#include <linux/init.h>

#include <asm/irq.h>
#include <asm/io.h>

static struct input_dev *button_dev;

static irqreturn_t button_interrupt(int irq, void *dummy)
{
    input_report_key(button_dev, BTN_0, inb(BUTTON_PORT) & 1);
    input_sync(button_dev);
    return IRQ_HANDLED;
}

static int __init button_init(void)
{
    int error;

    if (request_irq(BUTTON_IRQ, button_interrupt, 0, "button", NULL)) {
                printk(KERN_ERR "button.c: Can''t allocate irq %d\n", button_irq);
                return -EBUSY;
        }

    button_dev = input_allocate_device();
    if (!button_dev) {
        printk(KERN_ERR "button.c: Not enough memory\n");
        error = -ENOMEM;
        goto err_free_irq;
    }

    button_dev->evbit[0] = BIT_MASK(EV_KEY);
    button_dev->keybit[BIT_WORD(BTN_0)] = BIT_MASK(BTN_0);

    error = input_register_device(button_dev);
    if (error) {
        printk(KERN_ERR "button.c: Failed to register device\n");
        goto err_free_dev;
    }

    return 0;

 err_free_dev:
    input_free_device(button_dev);
 err_free_irq:
    free_irq(BUTTON_IRQ, button_interrupt);
    return error;
}

static void __exit button_exit(void)
{
        input_unregister_device(button_dev);
    free_irq(BUTTON_IRQ, button_interrupt);
}

module_init(button_init);
module_exit(button_exit);

1.1 What the example does
~~~~~~~~~~~~~~~~~~~~~~~~~

First it has to include the <linux/input.h> file, which interfaces to the
input subsystem. This provides all the definitions needed.

In the _init function, which is called either upon module load or when
booting the kernel, it grabs the required resources (it should also check
for the presence of the device).

Then it allocates a new input device structure with input_allocate_device()
and sets up input bitfields. This way the device driver tells the other
parts of the input systems what it is - what events can be generated or
accepted by this input device. Our example device can only generate EV_KEY
type events, and from those only BTN_0 event code. Thus we only set these
two bits. We could have used

    set_bit(EV_KEY, button_dev.evbit);
    set_bit(BTN_0, button_dev.keybit);

as well, but with more than single bits the first approach tends to be
shorter.

Then the example driver registers the input device structure by calling

    input_register_device(&button_dev);

This adds the button_dev structure to linked lists of the input driver and
calls device handler modules _connect functions to tell them a new input
device has appeared. input_register_device() may sleep and therefore must
not be called from an interrupt or with a spinlock held.

While in use, the only used function of the driver is

    button_interrupt()

which upon every interrupt from the button checks its state and reports it
via the

    input_report_key()

call to the input system. There is no need to check whether the interrupt
routine isn''t reporting two same value events (press, press for example) to
the input system, because the input_report_* functions check that
themselves.

Then there is the

    input_sync()

call to tell those who receive the events that we''ve sent a complete report.
This doesn''t seem important in the one button case, but is quite important
for for example mouse movement, where you don''t want the X and Y values
to be interpreted separately, because that''d result in a different movement.

1.2 dev->open() and dev->close()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In case the driver has to repeatedly poll the device, because it doesn''t
have an interrupt coming from it and the polling is too expensive to be done
all the time, or if the device uses a valuable resource (eg. interrupt), it
can use the open and close callback to know when it can stop polling or
release the interrupt and when it must resume polling or grab the interrupt
again. To do that, we would add this to our example driver:

static int button_open(struct input_dev *dev)
{
    if (request_irq(BUTTON_IRQ, button_interrupt, 0, "button", NULL)) {
                printk(KERN_ERR "button.c: Can''t allocate irq %d\n", button_irq);
                return -EBUSY;
        }

        return 0;
}

static void button_close(struct input_dev *dev)
{
        free_irq(IRQ_AMIGA_VERTB, button_interrupt);
}

static int __init button_init(void)
{
    ...
    button_dev->open = button_open;
    button_dev->close = button_close;
    ...
}

Note that input core keeps track of number of users for the device and
makes sure that dev->open() is called only when the first user connects
to the device and that dev->close() is called when the very last user
disconnects. Calls to both callbacks are serialized.

The open() callback should return a 0 in case of success or any nonzero value
in case of failure. The close() callback (which is void) must always succeed.

1.3 Basic event types
~~~~~~~~~~~~~~~~~~~~~

The most simple event type is EV_KEY, which is used for keys and buttons.
It''s reported to the input system via:

    input_report_key(struct input_dev *dev, int code, int value)

See linux/input.h for the allowable values of code (from 0 to KEY_MAX).
Value is interpreted as a truth value, ie any nonzero value means key
pressed, zero value means key released. The input code generates events only
in case the value is different from before.

In addition to EV_KEY, there are two more basic event types: EV_REL and
EV_ABS. They are used for relative and absolute values supplied by the
device. A relative value may be for example a mouse movement in the X axis.
The mouse reports it as a relative difference from the last position,
because it doesn''t have any absolute coordinate system to work in. Absolute
events are namely for joysticks and digitizers - devices that do work in an
absolute coordinate systems.

Having the device report EV_REL buttons is as simple as with EV_KEY, simply
set the corresponding bits and call the

    input_report_rel(struct input_dev *dev, int code, int value)

function. Events are generated only for nonzero value.

However EV_ABS requires a little special care. Before calling
input_register_device, you have to fill additional fields in the input_dev
struct for each absolute axis your device has. If our button device had also
the ABS_X axis:

    button_dev.absmin[ABS_X] = 0;
    button_dev.absmax[ABS_X] = 255;
    button_dev.absfuzz[ABS_X] = 4;
    button_dev.absflat[ABS_X] = 8;

Or, you can just say:

    input_set_abs_params(button_dev, ABS_X, 0, 255, 4, 8);

This setting would be appropriate for a joystick X axis, with the minimum of
0, maximum of 255 (which the joystick *must* be able to reach, no problem if
it sometimes reports more, but it must be able to always reach the min and
max values), with noise in the data up to +- 4, and with a center flat
position of size 8.

If you don''t need absfuzz and absflat, you can set them to zero, which mean
that the thing is precise and always returns to exactly the center position
(if it has any).

1.4 BITS_TO_LONGS(), BIT_WORD(), BIT_MASK()
~~~~~~~~~~~~~~~~~~~~~~~~~~

These three macros from bitops.h help some bitfield computations:

    BITS_TO_LONGS(x) - returns the length of a bitfield array in longs for
               x bits
    BIT_WORD(x)     - returns the index in the array in longs for bit x
    BIT_MASK(x)     - returns the index in a long for bit x

1.5 The id* and name fields
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The dev->name should be set before registering the input device by the input
device driver. It''s a string like ''Generic button device'' containing a
user friendly name of the device.

The id* fields contain the bus ID (PCI, USB, ...), vendor ID and device ID
of the device. The bus IDs are defined in input.h. The vendor and device ids
are defined in pci_ids.h, usb_ids.h and similar include files. These fields
should be set by the input device driver before registering it.

The idtype field can be used for specific information for the input device
driver.

The id and name fields can be passed to userland via the evdev interface.

1.6 The keycode, keycodemax, keycodesize fields
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

These three fields should be used by input devices that have dense keymaps.
The keycode is an array used to map from scancodes to input system keycodes.
The keycode max should contain the size of the array and keycodesize the
size of each entry in it (in bytes).

Userspace can query and alter current scancode to keycode mappings using
EVIOCGKEYCODE and EVIOCSKEYCODE ioctls on corresponding evdev interface.
When a device has all 3 aforementioned fields filled in, the driver may
rely on kernel''s default implementation of setting and querying keycode
mappings.

1.7 dev->getkeycode() and dev->setkeycode()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
getkeycode() and setkeycode() callbacks allow drivers to override default
keycode/keycodesize/keycodemax mapping mechanism provided by input core
and implement sparse keycode maps.

1.8 Key autorepeat
~~~~~~~~~~~~~~~~~~

... is simple. It is handled by the input.c module. Hardware autorepeat is
not used, because it''s not present in many devices and even where it is
present, it is broken sometimes (at keyboards: Toshiba notebooks). To enable
autorepeat for your device, just set EV_REP in dev->evbit. All will be
handled by the input system.

1.9 Other event types, handling output events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The other event types up to now are:

EV_LED - used for the keyboard LEDs.
EV_SND - used for keyboard beeps.

They are very similar to for example key events, but they go in the other
direction - from the system to the input device driver. If your input device
driver can handle these events, it has to set the respective bits in evbit,
*and* also the callback routine:

    button_dev->event = button_event;

int button_event(struct input_dev *dev, unsigned int type, unsigned int code, int value);
{
    if (type == EV_SND && code == SND_BELL) {
        outb(value, BUTTON_BELL);
        return 0;
    }
    return -1;
}

This callback routine can be called from an interrupt or a BH (although that
isn''t a rule), and thus must not sleep, and must not take too long to finish.

struct input_dev {
    const char *name;             //  input设备的名字
    const char *phys;              //  
    const char *uniq;              //
    struct input_id id;             //  

//  这些是用来表示该input设备能够上报的事件类型有哪些   是用位的方式来表示的
    unsigned long evbit[BITS_TO_LONGS(EV_CNT)];
    unsigned long keybit[BITS_TO_LONGS(KEY_CNT)];
    unsigned long relbit[BITS_TO_LONGS(REL_CNT)];
    unsigned long absbit[BITS_TO_LONGS(ABS_CNT)];
    unsigned long mscbit[BITS_TO_LONGS(MSC_CNT)];
    unsigned long ledbit[BITS_TO_LONGS(LED_CNT)];
    unsigned long sndbit[BITS_TO_LONGS(SND_CNT)];
    unsigned long ffbit[BITS_TO_LONGS(FF_CNT)];
    unsigned long swbit[BITS_TO_LONGS(SW_CNT)];

    unsigned int keycodemax;
    unsigned int keycodesize;
    void *keycode;
    int (*setkeycode)(struct input_dev *dev,
              unsigned int scancode, unsigned int keycode);
    int (*getkeycode)(struct input_dev *dev,
              unsigned int scancode, unsigned int *keycode);

    struct ff_device *ff;

    unsigned int repeat_key;
    struct timer_list timer;

    int sync;

    int abs[ABS_CNT];
    int rep[REP_MAX + 1];

    unsigned long key[BITS_TO_LONGS(KEY_CNT)];
    unsigned long led[BITS_TO_LONGS(LED_CNT)];
    unsigned long snd[BITS_TO_LONGS(SND_CNT)];
    unsigned long sw[BITS_TO_LONGS(SW_CNT)];

    int absmax[ABS_CNT];
    int absmin[ABS_CNT];
    int absfuzz[ABS_CNT];
    int absflat[ABS_CNT];
    int absres[ABS_CNT];

    int (*open)(struct input_dev *dev);              //    设备的open函数
    void (*close)(struct input_dev *dev);          
    int (*flush)(struct input_dev *dev, struct file *file);
    int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value);     //  上报事件

    struct input_handle *grab;

    spinlock_t event_lock;
    struct mutex mutex;

    unsigned int users;
    bool going_away;

    struct device dev;                 //  内置的device结构体变量

    struct list_head    h_list;    //  用来挂接input_dev 设备连接的所有handle 的一个链表头
    struct list_head    node;    //  作为链表节点挂接到  input_dev_list 链表上  (input_dev_list链表是input核心层维护的一个用来挂接所有input设备的一个链表头)
};

struct input_handler {

    void *private;            //  私有数据

    void (*event)(struct input_handle *handle, unsigned int type, unsigned int code, int value);   //  handler用于向上层上报输入事件的函数
    bool (*filter)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
    bool (*match)(struct input_handler *handler, struct input_dev *dev);            //   match 函数用来匹配handler 与 input_dev 设备
    int (*connect)(struct input_handler *handler, struct input_dev *dev, const struct input_device_id *id);   //  当handler 与 input_dev 匹配成功之后用来连接
    void (*disconnect)(struct input_handle *handle);          //  断开handler 与 input_dev 之间的连接
    void (*start)(struct input_handle *handle);                    

    const struct file_operations *fops;             //  一个file_operations 指针
    int minor;                                      //  该handler 的编号 (在input_table 数组中用来计算数组下标) input_table数组就是input子系统用来管理注册的handler的一个数据结构
    const char *name;                               //  handler的名字

    const struct input_device_id *id_table;      //  指向一个 input_device_id  类型的数组，用来进行与input设备匹配时用到的信息
 
    struct list_head    h_list;       //  用来挂接handler 上连接的所有handle 的一个链表头
    struct list_head    node;        //  作为一个链表节点挂接到 input_handler_list 链表上(input_handler_list 链表是一个由上层handler参维护的一个用来挂接所有注册的handler的链表头)
};

struct input_device_id {

    kernel_ulong_t flags;    //  这个flag 表示我们的这个 input_device_id 是用来匹配下面的4个情况的哪一项
                                    //  flag == 1表示匹配总线  2表示匹配供应商   4表示匹配产品  8表示匹配版本
    __u16 bustype;
    __u16 vendor;
    __u16 product;
    __u16 version;

    kernel_ulong_t evbit[INPUT_DEVICE_ID_EV_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t keybit[INPUT_DEVICE_ID_KEY_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t relbit[INPUT_DEVICE_ID_REL_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t absbit[INPUT_DEVICE_ID_ABS_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t mscbit[INPUT_DEVICE_ID_MSC_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t ledbit[INPUT_DEVICE_ID_LED_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t sndbit[INPUT_DEVICE_ID_SND_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t ffbit[INPUT_DEVICE_ID_FF_MAX / BITS_PER_LONG + 1];
    kernel_ulong_t swbit[INPUT_DEVICE_ID_SW_MAX / BITS_PER_LONG + 1];

    kernel_ulong_t driver_info;
};

static int __init input_init(void)
{
    int err;

    input_init_abs_bypass();

    err = class_register(&input_class);                //  创建设备类    /sys/class/input
    if (err) {
        printk(KERN_ERR "input: unable to register input_dev class\n");
        return err;
    }

    err = input_proc_init();           //    proc文件系统相关的初始化
    if (err)
        goto fail1;

    err = register_chrdev(INPUT_MAJOR, "input", &input_fops);       //   注册字符设备驱动   主设备号13   input_fops 中只实现了open函数，所以他的原理其实和misc其实是一样的
    if (err) {
        printk(KERN_ERR "input: unable to register char major %d", INPUT_MAJOR);
        goto fail2;
    }

    return 0;

 fail2:    input_proc_exit();
 fail1:    class_unregister(&input_class);
    return err;
}

struct input_dev *input_allocate_device(void)
{
    struct input_dev *dev;                 //   定义一个 input_dev  指针

    dev = kzalloc(sizeof(struct input_dev), GFP_KERNEL);   //  申请分配内存
    if (dev) {
        dev->dev.type = &input_dev_type;          //  确定input设备的 设备类型     input_dev_type
        dev->dev.class = &input_class;                //  确定input设备所属的设备类   class
        device_initialize(&dev->dev);                   //  input设备的初始化
        mutex_init(&dev->mutex);                        //  互斥锁初始化
        spin_lock_init(&dev->event_lock);            //  自旋锁初始化
        INIT_LIST_HEAD(&dev->h_list);                 //  input_dev -> h_list 链表初始化
        INIT_LIST_HEAD(&dev->node);                 //  input_dev -> node 链表初始化

        __module_get(THIS_MODULE);
    }

    return dev;
}

int input_register_device(struct input_dev *dev)      //  注册input输入设备
{
    static atomic_t input_no = ATOMIC_INIT(0);
    struct input_handler *handler;                          //  定义一个  input_handler 结构体指针
    const char *path;
    int error;

    /* Every input device generates EV_SYN/SYN_REPORT events. */
    __set_bit(EV_SYN, dev->evbit);                  //   每一个input输入设备都会发生这个事件

    /* KEY_RESERVED is not supposed to be transmitted to userspace. */
    __clear_bit(KEY_RESERVED, dev->keybit);  //  清除KEY_RESERVED 事件对应的bit位，也就是不传输这种类型的事件

    /* Make sure that bitmasks not mentioned in dev->evbit are clean. */
    input_cleanse_bitmasks(dev);           //   确保input_dev中的用来记录事件的变量中没有提到的位掩码是干净的。

    /*
     * 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.
     */
    init_timer(&dev->timer);
    if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD]) {
        dev->timer.data = (long) dev;
        dev->timer.function = input_repeat_key;
        dev->rep[REP_DELAY] = 250;
        dev->rep[REP_PERIOD] = 33;
    }

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

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

    dev_set_name(&dev->dev, "input%ld",                                  //   设置input设备对象的名字    input+数字
             (unsigned long) atomic_inc_return(&input_no) - 1);

    error = device_add(&dev->dev);         //   添加设备       例如:          /sys/devices/virtual/input/input0     
    if (error)
        return error;

    path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);  //  获取input设备对象所在的路径      /sys/devices/virtual/input/input_xxx   
    printk(KERN_INFO "input: %s as %s\n",
        dev->name ? dev->name : "Unspecified device", path ? path : "N/A");
    kfree(path);

    error = mutex_lock_interruptible(&input_mutex);
    if (error) {
        device_del(&dev->dev);
        return error;
    }

    list_add_tail(&dev->node, &input_dev_list);             //   链表挂接:    将 input_dev->node 作为节点挂接到 input_dev_list  链表上

    list_for_each_entry(handler, &input_handler_list, node)  //  遍历input_handler_list 链表上的所有handler
        input_attach_handler(dev, handler);                        //  将handler与input设备进行匹配

    input_wakeup_procfs_readers();                //  更新proc 文件系统

    mutex_unlock(&input_mutex);

    return 0;
}

static int input_attach_handler(struct input_dev *dev, struct input_handler *handler)
{
    const struct input_device_id *id;                //   定义一个input_device_id 的指针
    int error;

    id = input_match_device(handler, dev);   //  通过这个函数进行handler与input设备的匹配工作
    if (!id)
        return -ENODEV;

    error = handler->connect(handler, dev, id);  //  匹配成功则调用 handler 中的 connect 函数进行连接
    if (error && error != -ENODEV)
        printk(KERN_ERR
            "input: failed to attach handler %s to device %s, "
            "error: %d\n",
            handler->name, kobject_name(&dev->dev.kobj), error);

    return error;
}



static const struct input_device_id *input_match_device(struct input_handler *handler,
                            struct input_dev *dev)
{
    const struct input_device_id *id;            //   定义一个 input_device_id  指针
    int i;

    for (id = handler->id_table; id->flags || id->driver_info; id++) {  //  依次遍历handler->id_table 所指向的input_device_id 数组中的各个元素
                                                                                                                    //  依次进行下面的匹配过程
        if (id->flags & INPUT_DEVICE_ID_MATCH_BUS)         //    匹配总线
            if (id->bustype != dev->id.bustype)
                continue;

        if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR)  //  匹配供应商
            if (id->vendor != dev->id.vendor)
                continue;

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

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

    //    下面的这些是匹配我们上传的事件是否属实
        MATCH_BIT(evbit,  EV_MAX);
        MATCH_BIT(keybit, KEY_MAX);
        MATCH_BIT(relbit, REL_MAX);
        MATCH_BIT(absbit, ABS_MAX);
        MATCH_BIT(mscbit, MSC_MAX);
        MATCH_BIT(ledbit, LED_MAX);
        MATCH_BIT(sndbit, SND_MAX);
        MATCH_BIT(ffbit,  FF_MAX);
        MATCH_BIT(swbit,  SW_MAX);

        if (!handler->match || handler->match(handler, dev))
            return id;        //    如果数组中的某个匹配成功了就返回他的地址
    }

    return NULL;
}

#include <linux/init.h>            // __init   __exit
#include <linux/module.h>      // module_init  module_exit
#include <mach/regs-gpio.h>
#include <mach/gpio-bank.h>

#include <mach/gpio.h> 
#include <linux/leds.h>
#include <asm/string.h> 

#include <linux/platform_device.h>

#include <linux/input.h> 
#include "button_device_driver.h"

#define BUTTON_GPIO_CONFIG 0xFF

/* KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT
    * LEFT     -> EINT2    -> GPH0_2
    * DOWN     -> EINT3    -> GPH0_3
    * UP     -> KP_COL0 -> GPH2_0
    * RIGHT  -> KP_COL1 -> GPH2_1
    * MENU     -> KP_COL3 -> GPH2_3 (KEY_A)
    * BACK     -> KP_COL2 -> GPH2_2 (KEY_B)
    */

void s5pv210_button_release(struct device *dev);

struct gpioIRQ button_irq[] = 
{
    {
        "button_Left_IRQ",
        BUTTON_LEFT_IRQ,
        IRQF_TRIGGER_RISING|IRQF_TRIGGER_FALLING,
    },
    {
        "button_down_IRQ",
        BUTTON_DOWN_IRQ,
        IRQF_TRIGGER_RISING|IRQF_TRIGGER_FALLING,
    }
};
static struct s5pv210_button_platdata x210_button_pdata[] = {
    [0]={
        .name        = "button_Left",
        .gpio        = S5PV210_GPH0(2),
        .gpio_cfg    = BUTTON_GPIO_CONFIG,
        .button_code= KEY_LEFT,
        .button_irq    = &button_irq[0],
        },
    [1]={
        .name        = "button_down",
        .gpio        =  S5PV210_GPH0(3),
        .gpio_cfg    = BUTTON_GPIO_CONFIG,
        .button_code= KEY_DOWN,
        .button_irq    = &button_irq[1],
        }
};


static struct platform_device s5pv210_device_button = {
    .name    = "s5pv210-button",
    .id        = -1,
    .dev    = {
            .platform_data    = &x210_button_pdata,
            .release = s5pv210_button_release,
        },
};
void s5pv210_button_release(struct device *dev)
{
    printk(KERN_WARNING "s5pv210_button_release successful \n");
}

static int __init s5pv210_button_init(void)
{
    int ret = -1;
    printk(KERN_INFO "device.c : s5pv210_button_init successful \n");    
    ret = platform_device_register(&s5pv210_device_button);
    if (ret < 0) 
    {
        printk(KERN_WARNING "platform_add_devices fail \n");
    }
    return ret;
}

static void __exit s5pv210_button_exit(void)
{    
    printk(KERN_INFO "device.c : s5pv210_button_exit successful \n");

    platform_device_unregister(&s5pv210_device_button); 
}




module_init(s5pv210_button_init);
module_exit(s5pv210_button_exit);

// MODULE_xxx这种宏作用是用来添加模块描述信息
MODULE_LICENSE("GPL");                // 描述模块的许可证
MODULE_AUTHOR("musk");                // 描述模块的作者
MODULE_DESCRIPTION("x210 button device");    // 描述模块的介绍信息
MODULE_ALIAS("button_device");            // 描述模块的别名信息
        3.2.2. button_driver.c

#include <linux/input.h> 
#include <linux/module.h> 
#include <linux/init.h>
#include <asm/irq.h> 
#include <asm/io.h>

#include <mach/irqs.h>

#include <linux/gpio.h>
#include <linux/interrupt.h>
#include <linux/platform_device.h>

#include "button_device_driver.h"
#include <linux/kernel.h> 
/*
 * POWER  -> EINT1   -> GPH0_1
 * LEFT   -> EINT2   -> GPH0_2
 * DOWN   -> EINT3   -> GPH0_3
 * UP     -> KP_COL0 -> GPH2_0
 * RIGHT  -> KP_COL1 -> GPH2_1
 * MENU   -> KP_COL3 -> GPH2_3 (KEY_A)
 * BACK   -> KP_COL2 -> GPH2_2 (KEY_B)
 */

static struct input_dev *button_dev;


static irqreturn_t button_interrupt(int irq, void *dummy) 
{ 
    
    struct platform_device *pdev = (struct platform_device *)dummy;
    struct s5pv210_button_platdata *pdata = pdev->dev.platform_data;
    if(dummy == NULL)
    {
        printk("\n button_interrupt fail;irq = %d\n",irq);
        return -1;
    }
    printk("\n irq = %d\n",irq);
    if(irq == pdata[0].button_irq->irq)
    {
        s3c_gpio_cfgpin(pdata[0].gpio, S3C_GPIO_SFN(0x00));
        input_report_key(button_dev, pdata[0].button_code,!gpio_get_value(pdata[0].gpio));
        s3c_gpio_cfgpin(pdata[0].gpio, S3C_GPIO_SFN(0x0f));
    }
    if(irq == pdata[1].button_irq->irq)
    {
        s3c_gpio_cfgpin(pdata[1].gpio, S3C_GPIO_SFN(0x00));
        input_report_key(button_dev, pdata[1].button_code,!gpio_get_value(pdata[1].gpio));
        s3c_gpio_cfgpin(pdata[1].gpio, S3C_GPIO_SFN(0x0f));
    }
    input_sync(button_dev);

    return IRQ_HANDLED; 
}


static int s5pv210_button_probe(struct platform_device *pdev)
{
    int error,ret;
    struct s5pv210_button_platdata *pdata = pdev->dev.platform_data;
    printk(KERN_INFO "button_driver.c: s5pv210_button_probe successful\n");
    if (request_irq(pdata[0].button_irq->irq, button_interrupt, pdata[0].button_irq->irq_trigger, pdata[0].button_irq->name, pdev)) 
    { 
        printk(KERN_ERR "key-s5pv210.c: Can''t allocate irq %d\n", pdata[0].button_irq->irq);
        return -EBUSY;
    }
    ret = gpio_request(pdata[0].gpio, pdata[0].name);
    if(ret)
        printk("button-driver: request %s fail", pdata[0].name);
    s3c_gpio_cfgpin(pdata[0].gpio, S3C_GPIO_SFN(pdata[0].gpio_cfg));
    
    
    
    if (request_irq(pdata[1].button_irq->irq, button_interrupt, pdata[1].button_irq->irq_trigger, pdata[1].button_irq->name, pdev)) 
    { 
        printk(KERN_ERR "key-s5pv210.c: Can''t allocate irq %d\n", pdata[1].button_irq->irq);
        return -EBUSY;
    }
        ret = gpio_request(pdata[1].gpio, pdata[1].name);
    if(ret)
        printk(KERN_ERR "button-driver: request %s fail", pdata[1].name);
    s3c_gpio_cfgpin(pdata[1].gpio, S3C_GPIO_SFN(pdata[1].gpio_cfg));
    
    
    button_dev = input_allocate_device();
    if (!button_dev)    
    { 
        printk(KERN_ERR "button.c: Not enough memory\n");
        error = -ENOMEM;
        goto err_free_irq; 
    }
    
    set_bit(EV_KEY, button_dev->evbit);

    set_bit(pdata[0].button_code, button_dev->keybit);
    set_bit(pdata[1].button_code, button_dev->keybit);

    error = input_register_device(button_dev);
    if (error) 
    { 
        printk(KERN_ERR "button_driver.c: Failed to register device\n");
        goto err_free_dev; 
    }
    return 0;
 
 err_free_dev:
    input_free_device(button_dev);
    
 err_free_irq:
    free_irq(pdata[0].button_irq->irq, pdev);
    free_irq(pdata[1].button_irq->irq, pdev);
    gpio_free(pdata[0].gpio);
    gpio_free(pdata[1].gpio);
    
    return error;
}

static int s5pv210_button_remove(struct platform_device *pdev)
{
    struct s5pv210_button_platdata *pdata = pdev->dev.platform_data;
    printk(KERN_INFO "button_driver.c: s5pv210_button_remove successful\n");
    
    free_irq(IRQ_EINT2, pdev);
    free_irq(IRQ_EINT3, pdev);
    gpio_free(pdata[0].gpio);    
    gpio_free(pdata[1].gpio);    
    input_unregister_device(button_dev);

    
    return  0;
}

static struct platform_driver s5pv210_button_driver = {
    .probe        = s5pv210_button_probe,
    .remove        = s5pv210_button_remove,
    .driver        = {
        .name    = "s5pv210-button",
        .owner    = THIS_MODULE,
    }
};

static int __init s5pv210_button_init(void) 
{ 
    return platform_driver_register(&s5pv210_button_driver);
}
static void __exit s5pv210_button_exit(void)
{
    platform_driver_unregister(&s5pv210_button_driver);
}

module_init(s5pv210_button_init); 
module_exit(s5pv210_button_exit);

MODULE_AUTHOR("musk");
MODULE_DESCRIPTION("s5pv210 button driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("button-s5pv210");
        3.2.3. button_device_driver.h

#ifndef __BUTTON_DEVICE_DRIVER_H
#define __BUTTON_DEVICE_DRIVER_H 

#define BUTTON_LEFT_IRQ  IRQ_EINT2
#define BUTTON_DOWN_IRQ  IRQ_EINT3

#include <mach/irqs.h>
#include <linux/interrupt.h>

struct gpioIRQ {
    char            *name;
    unsigned int     irq;
    unsigned long    irq_trigger;

};
struct s5pv210_button_platdata {
    char            *name;

    unsigned int    gpio;
    unsigned int     gpio_cfg;
    unsigned int    button_code;
    struct gpioIRQ     *button_irq;
};

#endif /* __ASM_ARCH_LEDSGPIO_H */