USB鼠标驱动 usbmouse.c
原文链接：/Linux/-12/76197p7.htm
drivers/hid/usbhid/usbmouse.c
下面我们分析下USB鼠标驱动，鼠标输入HID类型，其数据传输采用中断URB，鼠标端点类型为IN。我们先看看这个驱动的模块加载部分。
static int __init usb_mouse_init(void){int retval = usb_register(&usb_mouse_driver);if (retval == 0)printk(KERN_INFO KBUILD_MODNAME ": " DRIVER_VERSION ":"DRIVER_DESC "\n");return retval;}
模块加载部分仍然是调用usb_register注册USB驱动，我们跟踪看看被注册的usb_mouse_driver
static struct usb_driver usb_mouse_driver = {.name= "usbmouse", //驱动名.probe= usb_mouse_probe,.disconnect= usb_mouse_disconnect,.id_table= usb_mouse_id_table, //支持项};
关于设备支持项我们前面已经讨论过了
static struct usb_device_id usb_mouse_id_table [] = {{ USB_INTERFACE_INFO(USB_INTERFACE_CLASS_HID, USB_INTERFACE_SUBCLASS_BOOT,USB_INTERFACE_PROTOCOL_MOUSE) },{ }/* Terminating entry */};MODULE_DEVICE_TABLE (usb, usb_mouse_id_table);
再细细看看USB_INTERFACE_INFO宏的定义
/*** USB_INTERFACE_INFO - macro used to describe a class of usb interfaces* @cl: bInterfaceClass value* @sc: bInterfaceSubClass value* @pr: bInterfaceProtocol value** This macro is used to create a struct usb_device_id that matches a* specific class of interfaces.*/#define USB_INTERFACE_INFO(cl, sc, pr) \.match_flags = USB_DEVICE_ID_MATCH_INT_INFO, \.bInterfaceClass = (cl), \.bInterfaceSubClass = (sc), \.bInterfaceProtocol = (pr)
根据宏，我们知道，我们设置的支持项包括接口类，接口子类，接口协议三个匹配项。
主要看看usb_driver中定义的probe函数
static int usb_mouse_probe(struct usb_interface *intf, const struct usb_device_id *id){struct usb_device *dev = interface_to_usbdev(intf);//由接口获取usb_devstruct usb_host_interface *interface;struct usb_endpoint_descriptor *endpoint;struct usb_mouse *mouse; //该驱动私有结构体struct input_dev *input_dev; //输入结构体int pipe, maxp;int error = -ENOMEM;interface = intf->cur_altsetting; //获取设置if (interface->desc.bNumEndpoints != 1) //鼠标端点只有1个return -ENODEV;endpoint = &interface->endpoint[0].desc; //获取端点描述符if (!usb_endpoint_is_int_in(endpoint)) //检查该端点是否是中断输入端点return -ENODEV;pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress); //建立中断输入端点maxp = usb_maxpacket(dev, pipe, usb_pipeout(pipe));//端点能传输的最大数据包(Mouse为4个)mouse = kzalloc(sizeof(struct usb_mouse), GFP_KERNEL); //分配usb_mouse结构体input_dev = input_allocate_device(); //分配input设备空间if (!mouse || !input_dev)goto fail1;mouse->data = usb_alloc_coherent(dev, 8, GFP_ATOMIC, &mouse->data_dma); //分配缓冲区if (!mouse->data)goto fail1;mouse->irq = usb_alloc_urb(0, GFP_KERNEL);//分配urbif (!mouse->irq)goto fail2;mouse->usbdev = dev; //填充mouse的usb_device结构体mouse->dev = input_dev;//填充mouse的input结构体if (dev->manufacturer) //复制厂商IDstrlcpy(mouse->name, dev->manufacturer, sizeof(mouse->name));if (dev->product) {//复制产品IDif (dev->manufacturer)strlcat(mouse->name, " ", sizeof(mouse->name));strlcat(mouse->name, dev->product, sizeof(mouse->name));}if (!strlen(mouse->name))snprintf(mouse->name, sizeof(mouse->name),"USB HIDBP Mouse %04x:%04x",le16_to_cpu(dev->descriptor.idVendor),le16_to_cpu(dev->descriptor.idProduct));usb_make_path(dev, mouse->phys, sizeof(mouse->phys));strlcat(mouse->phys, "/input0", sizeof(mouse->phys)); //获取usb_mouse的设备节点input_dev->name = mouse->name; //将鼠标名赋给内嵌input结构体input_dev->phys = mouse->phys; //将鼠标设备节点名赋给内嵌input结构体usb_to_input_id(dev, &input_dev->id); //将usb_driver的支持项拷贝给inputinput_dev->dev.parent = &intf->dev;input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);//支持按键事件和相对坐标事件input_dev->keybit[BIT_WORD(BTN_MOUSE)] = BIT_MASK(BTN_LEFT) |BIT_MASK(BTN_RIGHT) | BIT_MASK(BTN_MIDDLE); //表明按键值包括左键、中键和右键input_dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y);//表明相对坐标包括X坐标和Y坐标input_dev->keybit[BIT_WORD(BTN_MOUSE)] |= BIT_MASK(BTN_SIDE) |BIT_MASK(BTN_EXTRA);//表明除了左键、右键和中键，还支持其他按键input_dev->relbit[0] |= BIT_MASK(REL_WHEEL); //表明还支持中键滚轮的滚动值input_set_drvdata(input_dev, mouse); //将mouse设为input的私有数据input_dev->open = usb_mouse_open;//input设备的open操作函数input_dev->close = usb_mouse_close;usb_fill_int_urb(mouse->irq, dev, pipe, mouse->data,(maxp > 8 ? 8 : maxp),usb_mouse_irq, mouse, endpoint->bInterval); //填充urbmouse->irq->transfer_dma = mouse->data_dma;mouse->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP; //使用transfer_dmaerror = input_register_device(mouse->dev); //注册input设备if (error)goto fail3;usb_set_intfdata(intf, mouse);return 0;fail3:usb_free_urb(mouse->irq);fail2:usb_free_coherent(dev, 8, mouse->data, mouse->data_dma);fail1:input_free_device(input_dev);kfree(mouse);return error;}
在探讨probe实现的功能时，我们先看看urb填充函数usb_fill_int_urb
/*** usb_fill_int_urb - macro to help initialize a interrupt urb* @urb: pointer to the urb to initialize.* @dev: pointer to the struct usb_device for this urb.* @pipe: the endpoint pipe* @transfer_buffer: pointer to the transfer buffer* @buffer_length: length of the transfer buffer* @complete_fn: pointer to the usb_complete_t function* @context: what to set the urb context to.* @interval: what to set the urb interval to, encoded like*the endpoint descriptor's bInterval value.** Initializes a interrupt urb with the proper information needed to submit* it to a device.** Note that High Speed and SuperSpeed interrupt endpoints use a logarithmic* encoding of the endpoint interval, and express polling intervals in* microframes (eight per millisecond) rather than in frames (one per* millisecond).** Wireless USB also uses the logarithmic encoding, but specifies it in units of* 128us instead of 125us. For Wireless USB devices, the interval is passed* through to the host controller, rather than being translated into microframe* units.*/static inline void usb_fill_int_urb(struct urb *urb,struct usb_device *dev,unsigned int pipe,void *transfer_buffer,int buffer_length,usb_complete_t complete_fn,void *context,int interval){urb->dev = dev;urb->pipe = pipe;urb->transfer_buffer = transfer_buffer;urb->transfer_buffer_length = buffer_length;urb->complete = complete_fn;urb->context = context;if (dev->speed == USB_SPEED_HIGH || dev->speed == USB_SPEED_SUPER)urb->interval = 1 << (interval - 1);elseurb->interval = interval;urb->start_frame = -1;}
其实probe主要是初始化usb设备和input设备，终极目标是为了完成urb的提交和input设备的注册。由于注册为input设备类型，那么当用户层open打开设备时候，最终会调用input中的open实现打开，我们看看input中open的实现
static int usb_mouse_open(struct input_dev *dev){struct usb_mouse *mouse = input_get_drvdata(dev); //获取私有数据mouse->irq->dev = mouse->usbdev;//获取utb指针if (usb_submit_urb(mouse->irq, GFP_KERNEL)) //提交urbreturn -EIO;return 0;}
当用户层open打开这个USB鼠标后，我们就已经将urb提交给了USB core，那么根据USB数据处理流程知道，当处理完毕后，USB core会通知USB设备驱动程序，这里我们是响应中断服务程序，这就相当于该URB的回调函数。我们在提交urb时候定义了中断服务程序 usb_mouse_irq，我们跟踪看看
static void usb_mouse_irq(struct urb *urb){struct usb_mouse *mouse = urb->context;signed char *data = mouse->data;struct input_dev *dev = mouse->dev;int status;switch (urb->status) {case 0:/* success */break;case -ECONNRESET:/* unlink */case -ENOENT:case -ESHUTDOWN:return;/* -EPIPE: should clear the halt */default:/* error */goto resubmit; //数据处理没成功，重新提交urb}input_report_key(dev, BTN_LEFT, data[0] & 0x01); //左键input_report_key(dev, BTN_RIGHT, data[0] & 0x02); //input_report_key(dev, BTN_MIDDLE, data[0] & 0x04); //input_report_key(dev, BTN_SIDE, data[0] & 0x08); //input_report_key(dev, BTN_EXTRA, data[0] & 0x10); //input_report_rel(dev, REL_X,data[1]); //鼠标的水平位移input_report_rel(dev, REL_Y,data[2]); //鼠标的垂直位移input_report_rel(dev, REL_WHEEL, data[3]); //鼠标滚轮的滚动值input_sync(dev);//同步事件，完成一次上报resubmit:status = usb_submit_urb (urb, GFP_ATOMIC); //再次提交urb，等待下次响应if (status)err ("can't resubmit intr, %s-%s/input0, status %d",mouse->usbdev->bus->bus_name,mouse->usbdev->devpath, status);}
根据上面的中断服务程序，我们应该知道，系统是周期性地获取鼠标的事件信息，因此在URB回调函数的末尾再次提交URB请求块，这样又会调用新的回调函数，周而复始。在回调函数中提交URB只能是GFP_ATOMIC优先级，因为URB回调函数运行于中断上下文中禁止导致睡眠的行为。而在提交URB 过程中可能会需要申请内存、保持信号量，这些操作或许会导致USB内核睡眠。
最后我们再看看这个驱动的私有数据mouse的定义
struct usb_mouse {char name[128]; //名字char phys[64]; //设备节点struct usb_device *usbdev; //内嵌usb_device设备struct input_dev *dev;//内嵌input_dev设备struct urb *irq; //urb结构体signed char *data;//transfer_buffer缓冲区dma_addr_t data_dma; //transfer _dma缓冲区};
在上面这个结构体中，每一个成员的作用都应该很清楚了，尤其最后两个的使用区别和作用，前面也已经说过。
如果最终需要测试这个USB鼠标驱动，需要在内核中配置USB支持、对HID接口的支持、对OHCI HCD驱动的支持。另外，将驱动移植到开发板之后，由于采用的是input设备模型，所以还需要开发板带LCD屏才能测试。
