int usb_get_device_descriptor (struct usb_device * dev);
Updates the copy of the device descriptor stored in the device structure, which dedicates space for this purpose. Note that several fields are converted to the host CPU's byte order: the USB version (bcdUSB), and vendors product and version fields (idVendor, idProduct, and bcdDevice). That lets device drivers compare against non-byteswapped constants.
There's normally no need to use this call, although some devices will change their descriptors after events like updating firmware.
This call is synchronous, and may not be used in an interrupt context.
Returns the number of bytes received on success, or else the status code returned by the underlying usb_control_msg call.