USB键盘驱动

键盘是一种输入型的设备，基于USB接口，内核提供了USB键盘的驱动，定义在drivers/hid/usbhid/usbkhd.c

一、USB键盘驱动的结构
定义了USB键盘的usb_driver的实例

static struct usb_driver usb_kbd_driver = {
    .name =        "usbkbd",//驱动名
    .probe =    usb_kbd_probe,//探测方法
    .disconnect =    usb_kbd_disconnect,//断开连接方法
    .id_table =    usb_kbd_id_table,//支持的设备ID
};

驱动支持的设备ID列表，定义了驱动支持的设备ID

static struct usb_device_id usb_kbd_id_table [] = {
    { USB_INTERFACE_INFO(USB_INTERFACE_CLASS_HID, USB_INTERFACE_SUBCLASS_BOOT,
        USB_INTERFACE_PROTOCOL_KEYBOARD) },
    { }                        /* Terminating entry */
};
MODULE_DEVICE_TABLE (usb, usb_kbd_id_table);

二、驱动的加载和卸载方法

//驱动加载方法
static int __init usb_kbd_init(void)
{
    //注册USB驱动
    int result = usb_register(&usb_kbd_driver);
    if (result == 0)
        printk(KERN_INFO KBUILD_MODNAME ": " DRIVER_VERSION ":"
                DRIVER_DESC "\n");
    return result;
}
//驱动卸载方法
static void __exit usb_kbd_exit(void)
{
    //注销USB驱动
    usb_deregister(&usb_kbd_driver);
}

三、探测方法
当USB键盘插入USB接口，USB核心通过USB键盘的属性匹配对应的驱动，找到对应的驱动后会调用驱动的探测方法

static int usb_kbd_probe(struct usb_interface *iface,
             const struct usb_device_id *id)
{
    //通过接口得到USB设备结构
    struct usb_device *dev = interface_to_usbdev(iface);
    struct usb_host_interface *interface;
    struct usb_endpoint_descriptor *endpoint;
    struct usb_kbd *kbd;
    struct input_dev *input_dev;
    int i, pipe, maxp;
    int error = -ENOMEM;
    //获得当前激活的接口
    interface = iface->cur_altsetting;
    //判断当前接口的端点数是否为1
    if (interface->desc.bNumEndpoints != 1)
        return -ENODEV;
    //获得端点的描述
    endpoint = &interface->endpoint[0].desc;
    //判断端点是否为中断端点
    if (!usb_endpoint_is_int_in(endpoint))
        return -ENODEV;
    //创建一个管道
    pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress);
    //获得端点传输的最大数据包大小
    maxp = usb_maxpacket(dev, pipe, usb_pipeout(pipe));

    kbd = kzalloc(sizeof(struct usb_kbd), GFP_KERNEL);
    //创建input_dev结构
    input_dev = input_allocate_device();
    if (!kbd || !input_dev)
        goto fail1;
    //分配usb_kbd内存空间
    if (usb_kbd_alloc_mem(dev, kbd))
        goto fail2;
    //为usb_kbd结构赋值
    kbd->usbdev = dev;
    kbd->dev = input_dev;
    //获得制造商
    if (dev->manufacturer)
        strlcpy(kbd->name, dev->manufacturer, sizeof(kbd->name));
    //获得产品名
    if (dev->product) {
        if (dev->manufacturer)
            strlcat(kbd->name, " ", sizeof(kbd->name));
        strlcat(kbd->name, dev->product, sizeof(kbd->name));
    }

    if (!strlen(kbd->name))
        snprintf(kbd->name, sizeof(kbd->name),
             "USB HIDBP Keyboard %04x:%04x",
             le16_to_cpu(dev->descriptor.idVendor),
             le16_to_cpu(dev->descriptor.idProduct));

    usb_make_path(dev, kbd->phys, sizeof(kbd->phys));
    strlcat(kbd->phys, "/input0", sizeof(kbd->phys));
    //为input_dev结构赋值
    input_dev->name = kbd->name;
    input_dev->phys = kbd->phys;
    usb_to_input_id(dev, &input_dev->id);
    input_dev->dev.parent = &iface->dev;

    input_set_drvdata(input_dev, kbd);

    input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_LED) |
        BIT_MASK(EV_REP);
    input_dev->ledbit[0] = BIT_MASK(LED_NUML) | BIT_MASK(LED_CAPSL) |
        BIT_MASK(LED_SCROLLL) | BIT_MASK(LED_COMPOSE) |
        BIT_MASK(LED_KANA);
    //设置键编码
    for (i = 0; i < 255; i++)
        set_bit(usb_kbd_keycode[i], input_dev->keybit);
    clear_bit(0, input_dev->keybit);

    input_dev->event = usb_kbd_event;
    input_dev->open = usb_kbd_open;
    input_dev->close = usb_kbd_close;
    //中断urb初始化
    usb_fill_int_urb(kbd->irq, dev, pipe,
             kbd->new, (maxp > 8 ? 8 : maxp),
             usb_kbd_irq, kbd, endpoint->bInterval);
    kbd->irq->transfer_dma = kbd->new_dma;
    kbd->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

    kbd->cr->bRequestType = USB_TYPE_CLASS | USB_RECIP_INTERFACE;
    kbd->cr->bRequest = 0x09;
    kbd->cr->wValue = cpu_to_le16(0x200);
    kbd->cr->wIndex = cpu_to_le16(interface->desc.bInterfaceNumber);
    kbd->cr->wLength = cpu_to_le16(1);
    //控制urb初始化
    usb_fill_control_urb(kbd->led, dev, usb_sndctrlpipe(dev, 0),
             (void *) kbd->cr, kbd->leds, 1,
                 usb_kbd_led, kbd);
    kbd->led->transfer_dma = kbd->leds_dma;
    kbd->led->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
    //注册输入设备
    error = input_register_device(kbd->dev);
    if (error)
        goto fail2;

    usb_set_intfdata(iface, kbd);
    device_set_wakeup_enable(&dev->dev, 1);
    return 0;

fail2:
    usb_kbd_free_mem(dev, kbd);
fail1:
    input_free_device(input_dev);
    kfree(kbd);
    return error;
}

探测方法的功能为分配一个input_dev结构并初始化input_dev结构；分配中断URB，中断初始化URB；分配控制URB，
控制初始化URB；注册输入设备

四、断开连接的方法

static void usb_kbd_disconnect(struct usb_interface *intf)
{
    struct usb_kbd *kbd = usb_get_intfdata (intf);

    usb_set_intfdata(intf, NULL);
    if (kbd) {
        //取消urb传递
        usb_kill_urb(kbd->irq);
        //注销input设备
        input_unregister_device(kbd->dev);
        //释放USB DMA空间
        usb_kbd_free_mem(interface_to_usbdev(intf), kbd);
        kfree(kbd);
    }
}

五、中断URB回调方法

static void usb_kbd_irq(struct urb *urb)
{
    struct usb_kbd *kbd = urb->context;
    int i;
    //判断URB状态
    switch (urb->status) {
    case 0:            /* success */
        break;
    case -ECONNRESET:    /* unlink */
    case -ENOENT:
    case -ESHUTDOWN:
        return;
    /* -EPIPE: should clear the halt */
    default:        /* error */
        goto resubmit;
    }
    //向输入子系统核心提交事件
    for (i = 0; i < 8; i++)
        input_report_key(kbd->dev, usb_kbd_keycode[i + 224], (kbd->new[0] >> i) & 1);

    for (i = 2; i < 8; i++) {

        if (kbd->old[i] > 3 && memscan(kbd->new + 2, kbd->old[i], 6) == kbd->new + 8) {
            if (usb_kbd_keycode[kbd->old[i]])
                input_report_key(kbd->dev, usb_kbd_keycode[kbd->old[i]], 0);
            else
                hid_info(urb->dev,
                     "Unknown key (scancode %#x) released.\n",
                     kbd->old[i]);
        }

        if (kbd->new[i] > 3 && memscan(kbd->old + 2, kbd->new[i], 6) == kbd->old + 8) {
            if (usb_kbd_keycode[kbd->new[i]])
                input_report_key(kbd->dev, usb_kbd_keycode[kbd->new[i]], 1);
            else
                hid_info(urb->dev,
                     "Unknown key (scancode %#x) released.\n",
                     kbd->new[i]);
        }
    }
    //同步事件
    input_sync(kbd->dev);

    memcpy(kbd->old, kbd->new, 8);

resubmit:
    //重新提交事件
    i = usb_submit_urb (urb, GFP_ATOMIC);
    if (i)
        hid_err(urb->dev, "can't resubmit intr, %s-%s/input0, status %d",
            kbd->usbdev->bus->bus_name,
            kbd->usbdev->devpath, i);
}

六、控制URB回调方法

static void usb_kbd_led(struct urb *urb)
{
    struct usb_kbd *kbd = urb->context;
    //判断URB状态
    if (urb->status)
        hid_warn(urb->dev, "led urb status %d received\n",
             urb->status);

    if (*(kbd->leds) == kbd->newleds)
        return;

    *(kbd->leds) = kbd->newleds;
    kbd->led->dev = kbd->usbdev;
    if (usb_submit_urb(kbd->led, GFP_ATOMIC))
        hid_err(urb->dev, "usb_submit_urb(leds) failed\n");
}

七、输入设备的事件处理方法

static int usb_kbd_event(struct input_dev *dev, unsigned int type,
             unsigned int code, int value)
{
    struct usb_kbd *kbd = input_get_drvdata(dev);

    if (type != EV_LED)
        return -1;

    kbd->newleds = (!!test_bit(LED_KANA, dev->led) << 3) | (!!test_bit(LED_COMPOSE, dev->led) << 3) |
         (!!test_bit(LED_SCROLLL, dev->led) << 2) | (!!test_bit(LED_CAPSL, dev->led) << 1) |
         (!!test_bit(LED_NUML, dev->led));

    if (kbd->led->status == -EINPROGRESS)
        return 0;

    if (*(kbd->leds) == kbd->newleds)
        return 0;

    *(kbd->leds) = kbd->newleds;
    kbd->led->dev = kbd->usbdev;
    if (usb_submit_urb(kbd->led, GFP_ATOMIC))
        pr_err("usb_submit_urb(leds) failed\n");

    return 0;
}

USB键盘驱动使用了中断URB和控制URB