Analysis of USB Device Driver

static const 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);
static struct usb_driver usb_mouse_driver = {  .name    = "usbmouse",  .probe    = usb_mouse_probe,  .disconnect  = usb_mouse_disconnect,  .id_table  = usb_mouse_id_table,};
module_usb_driver(usb_mouse_driver);

static int usb_mouse_probe(struct usb_interface *intf, const struct usb_device_id *id){  struct usb_device *dev = interface_to_usbdev(intf);  struct usb_host_interface *interface;  struct usb_endpoint_descriptor *endpoint;  struct usb_mouse *mouse;  struct input_dev *input_dev;  int pipe, maxp;  int error = -ENOMEM;
  interface = intf->cur_altsetting;
  if (interface->desc.bNumEndpoints != 1)    return -ENODEV;    // Get endpoint descriptor  endpoint = &interface->endpoint[0].desc;    // Check if the endpoint is interrupt input  if (!usb_endpoint_is_int_in(endpoint))    return -ENODEV;   // Get communication pipe via endpoint address  pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress);   // Get maximum data packet size  maxp = usb_maxpacket(dev, pipe, usb_pipeout(pipe));
  mouse = kzalloc(sizeof(struct usb_mouse), GFP_KERNEL);  input_dev = input_allocate_device(); // Allocate an input device
    // Allocate a buffer with the same size as DMA    // mouse->data_dma: the DMA address corresponding to the buffer, which is of type u32  mouse->data = usb_alloc_coherent(dev, 8, GFP_ATOMIC, &mouse->data_dma);
   // Allocate URB  mouse->irq = usb_alloc_urb(0, GFP_KERNEL);
  mouse->usbdev = dev; // Save usb_device  mouse->dev = input_dev; // Save input_device    // Device manufacturer and product name  if (dev->manufacturer)    strlcpy(mouse->name, dev->manufacturer, sizeof(mouse->name));
  if (dev->product) {    if (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));    // Set input device  input_dev->name = mouse->name;  input_dev->phys = mouse->phys;  usb_to_input_id(dev, &input_dev->id);  input_dev->dev.parent = &intf->dev;
  input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);  input_dev->keybit[BIT_WORD(BTN_MOUSE)] = BIT_MASK(BTN_LEFT) |    BIT_MASK(BTN_RIGHT) | BIT_MASK(BTN_MIDDLE);  input_dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y);  input_dev->keybit[BIT_WORD(BTN_MOUSE)] |= BIT_MASK(BTN_SIDE) |    BIT_MASK(BTN_EXTRA);  input_dev->relbit[0] |= BIT_MASK(REL_WHEEL);
  input_set_drvdata(input_dev, mouse);    // Set the open and close functions for the input device  input_dev->open = usb_mouse_open;  input_dev->close = usb_mouse_close;    // Initialize URB  usb_fill_int_urb(mouse->irq, dev, pipe, mouse->data,       (maxp > 8 ? 8 : maxp),       usb_mouse_irq, mouse, endpoint->bInterval);  mouse->irq->transfer_dma = mouse->data_dma; // DMA address  mouse->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;    // Register input device  error = input_register_device(mouse->dev);    // Save private data  usb_set_intfdata(intf, mouse);  return 0; // Omitted error handling...}

static void usb_mouse_disconnect(struct usb_interface *intf){  struct usb_mouse *mouse = usb_get_intfdata (intf);    // Release various resources  usb_set_intfdata(intf, NULL);  if (mouse) {    usb_kill_urb(mouse->irq);    input_unregister_device(mouse->dev); // Unregister input device    usb_free_urb(mouse->irq);    usb_free_coherent(interface_to_usbdev(intf), 8, mouse->data, mouse->data_dma);    kfree(mouse);  }}

static int usb_mouse_open(struct input_dev *dev){  struct usb_mouse *mouse = input_get_drvdata(dev);
  mouse->irq->dev = mouse->usbdev;    // Submit URB  if (usb_submit_urb(mouse->irq, GFP_KERNEL))    return -EIO;
  return 0;}
static void usb_mouse_close(struct input_dev *dev){  struct usb_mouse *mouse = input_get_drvdata(dev);    // Cancel URB  usb_kill_urb(mouse->irq);}

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;  }    // Report events to upper layers  input_report_key(dev, BTN_LEFT,   data[0] & 0x01);  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]);  input_report_rel(dev, REL_Y,     data[2]);  input_report_rel(dev, REL_WHEEL, data[3]);
  input_sync(dev); resubmit:    // Resubmit URB  status = usb_submit_urb (urb, GFP_ATOMIC);  //......}