Linux/Android——input子系统核心 (三)

   之前的博客有涉及到linux的input子系统,这里学习记录一下input模块.

input子系统,作为管理输入设备与系统进行交互的中枢,任何的输入设备驱动都要通过input向内核注册其设备,

常用的输入设备也就是鼠标,键盘,触摸屏。

稍微细分一点整个输入体系,就是 硬件驱动层input核心中转层事件处理层.层次之间传递都以event事件的形式,这其中input连接上下层,分别提供接口.

之前有分析usbtouchscreen的驱动,也就是硬件驱动部分,这里简单记录一下input核心中转处理 input.c .


                                              撰写不易,转载需注明出处:http://blog.csdn.net/jscese/article/details/42123673

input_init:

 源码位于/kernel/drivers/input/input.c ,模块初始调用口subsys_initcall(input_init),

由kernel启动的时候由kernel_init——>do_basic_setup();——>do_initcalls调用到,这个启动逻辑,后续有机会去学习一下,

这里首先调用到初始函数:

static int __init input_init(void)
{
    int err;

    err = class_register(&input_class); //注册input class,可在/sys/class下看到对应节点文件
    if (err) {
        pr_err("unable to register input_dev class\n");
        return err;
    }

    err = input_proc_init(); //proc fs的下的一些初始操作,函数原型在input.c,可查看/proc/bus/input
    if (err)
        goto fail1;

    err = register_chrdev(INPUT_MAJOR, "input", &input_fops); // 注册input字符设备,主节点为INPUT_MAJOR==13,可以去input_fops里看注册函数,注册到/dev/input
    if (err) {
        pr_err("unable to register char major %d", INPUT_MAJOR);
        goto fail2;
    }

    return 0;

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

这就是最开始的初始化过程了.


可以看下注册方法函数:

static const struct file_operations input_fops = {
    .owner = THIS_MODULE,
    .open = input_open_file,
    .llseek = noop_llseek,
};

这里面关注open file方法即可,后面分析。


input.c中还有很多其它的接口以及全局数据,后面陆续联通,先从设备驱动最先调用到的注册 input_register_device


input_register_device:

/**
 * 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)
{
    static atomic_t input_no = ATOMIC_INIT(0);  
        //这个原子变量,代表总共注册的input设备,每注册一个加1,因为是静态变量,所以每次调用都不会清零的
    struct input_handler *handler;
    const char *path;
    int error;

    __set_bit(EV_SYN, dev->evbit);  //EN_SYN 这个是设备都要支持的事件类型,所以要设置

    /*
     * 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.
     */
        // 这个内核定时器是为了重复按键而设置的
    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;
        //如果没有定义有关重复按键的相关值,就用内核默认的
    }

    if (!dev->getkeycode)
        dev->getkeycode = input_default_getkeycode;
    if (!dev->setkeycode)
        dev->setkeycode = input_default_setkeycode;
        //以上设置的默认函数由input核心提供
    dev_set_name(&dev->dev, "input%ld",
             (unsigned long) atomic_inc_return(&input_no) - 1);
        //设置input_dev中device的名字,这个名字会在/class/input中出现
    error = device_add(&dev->dev);
        //将device加入到linux设备模型中去
    if (error)
        return error;

    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);
        //这个得到路径名称,并打印出来
    error = mutex_lock_interruptible(&input_mutex);
    if (error) {
        device_del(&dev->dev);
        return error;
    }

    list_add_tail(&dev->node, &input_dev_list);
        // 将新分配的input设备连接到input_dev_list链表上
    list_for_each_entry(handler, &input_handler_list, node)
        input_attach_handler(dev, handler);
        //遍历input_handler_list链表,配对 input_dev 和 input_handler
        //input_attach_handler 这个函数是配对的关键,下面将详细分析
    input_wakeup_procfs_readers();
        // 和proc文件系统有关,暂时不考虑
    mutex_unlock(&input_mutex);

    return 0;
   }


可以看到前面都是一些初始设置,加入到input.c 的全局input_dev 链表里面,同时下面就行匹配对应handler的时候需要遍历 handler 链表:

static LIST_HEAD(input_dev_list);
static LIST_HEAD(input_handler_list);

可以看到用到了一个 list_for_each_entry, 刚开始看到还没看懂,这是一个宏定义,原型是在/kernel/include/linux/list.h:

/**
 * list_for_each_entry    -    iterate over list of given type
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 */
#define list_for_each_entry(pos, head, member)                \
    for (pos = list_entry((head)->next, typeof(*pos), member);    \
         &pos->member != (head);     \    //就是个for循环,跳出条件遍历了一遍,又回到链表头
         pos = list_entry(pos->member.next, typeof(*pos), member))


input_attach_handler(dev, handler)则是匹配这个要注册dev的handler:

static int input_attach_handler(struct input_dev *dev, struct input_handler *handler)
{
    const struct input_device_id *id;
    int error;

    id = input_match_device(handler, dev); //返回匹配的id,类型是struct input_device_id
    if (!id)
        return -ENODEV;

    error = handler->connect(handler, dev, id); ////配对成功调用handler的connect函数,这个函数在事件处理器中定义,主要生成一个input_handle结构,并初始化,还生成一个事件处理器相关的设备结构
    if (error && error != -ENODEV)
        pr_err("failed to attach handler %s to device %s, error: %d\n",
               handler->name, kobject_name(&dev->dev.kobj), error);

    return error;
}


可以看下匹配 id 的结构:

struct input_device_id {

	kernel_ulong_t flags;

	__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;
};


有两个函数input_match_device 以及 下面的 connect需要了解:


input_match_device:

static const struct input_device_id *input_match_device(struct input_handler *handler,
                            struct input_dev *dev)
{
    const struct input_device_id *id;
    int i;

    for (id = handler->id_table; id->flags || id->driver_info; id++) {

        if (id->flags & INPUT_DEVICE_ID_MATCH_BUS)  //匹配总线id
            if (id->bustype != dev->id.bustype)
                continue;

        if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR)  //匹配生产商id
            if (id->vendor != dev->id.vendor)
                continue;

        if (id->flags & INPUT_DEVICE_ID_MATCH_PRODUCT) //匹配产品id
            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;

        MATCH_BIT(evbit,  EV_MAX);  //匹配id的evbit和input_dev中evbit的各个位,如果不匹配则continue,数组中下一个设备
        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;
    }

    return NULL;
}

MATCH_bit 原型:

#define MATCH_BIT(bit, max) \
		for (i = 0; i < BITS_TO_LONGS(max); i++) \
			if ((id->bit[i] & dev->bit[i]) != id->bit[i]) \
				break; \
		if (i != BITS_TO_LONGS(max)) \
			continue;

可以看到这么多步的目的除了初始以及添加input_dev到链表,就是为了去匹配 input_handler_list 中对应的handler

匹配的最终是需要比对handler以及input_dev中的 id,其中input_dev 中的id类型为 input_id

struct input_id {
	__u16 bustype;
	__u16 vendor;
	__u16 product;
	__u16 version;
};

这跟上面 input_handler 结构里面的 input_device_id 匹配id 变量,来确认 handler!

在最开始的时候就有提到,整个input输入体系,分三个层次,现在的input核心层做的事就是:

在硬件驱动层调用 input_register_device时 ,往内核注册驱动的同时,根据硬件的相关id去匹配 适用的事件处理层(input_handler)!

这里匹配上之后就会调用对应 input_handler 的connect 函数。


input_handler:

input_dev 变量代表的是硬件设备,前文Linux/Android——输入子系统input_event传递 (二)中有介绍

input_handler 变量代表的是事件处理器

同样在input.h 中定义:

/**
 * 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);  //上面就是调用这个函数指针
	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; //这个就是上面说到的 会跟input_dev中的input_id 比对 id项的

	struct list_head	h_list;
	struct list_head	node;
};

这个结构详细的含义,注释有。

这个结构里面暂时只需要理解的:

注册input_dev ,在事件处理数据链表里面匹配上 input_handler ,就会调用其 *connect 函数指针 进行连接,

将input_dev 跟 input_handler 进行绑定, 后续的运作事件的handler处理将会走这个input_handler的 *event !

在上篇input_event 传递中最后调用到event阶段.


这里简单记录到这里,下篇介绍input_handler 的处理机制~




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