O valor de bInterfaceProtocol é fixo ou decidido pelo Kernel?

Question

Digamos que:

$ ls -l /dev/input/by-id
lrwxrwxrwx 1 root root 10 Feb 10 03:47 usb-Logitech_USB_Keyboard-event-if01 -> ../event22
lrwxrwxrwx 1 root root 10 Feb 10 03:47 usb-Logitech_USB_Keyboard-event-kbd -> ../event21
$ ls -l /dev/input/by-path/
lrwxrwxrwx 1 root root 10 Feb 10 03:47 pci-0000:00:14.0-usb-0:1.1:1.0-event-kbd -> ../event21
lrwxrwxrwx 1 root root 10 Feb 10 03:47 pci-0000:00:14.0-usb-0:1.1:1.1-event -> ../event22

Sei que o número de interface 1 (event22) acima não é funcional porque bInterfaceProtocol é None para bInterfaceNumber 1 :

$ sudo lsusb -v -d 046d:c31c

Bus 002 Device 005: ID 046d:c31c Logitech, Inc. Keyboard K120
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               1.10
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0         8
  idVendor           0x046d Logitech, Inc.
  idProduct          0xc31c Keyboard K120
  bcdDevice           64.00
  iManufacturer           1 Logitech
  iProduct                2 USB Keyboard
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           59
    bNumInterfaces          2
    bConfigurationValue     1
    iConfiguration          3 U64.00_B0001
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower               90mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      1 Boot Interface Subclass
      bInterfaceProtocol      1 Keyboard
      iInterface              2 USB Keyboard
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.10
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength      65
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval              10
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      0 No Subclass
      bInterfaceProtocol      0 None
      iInterface              2 USB Keyboard
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.10
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength     159
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0004  1x 4 bytes
        bInterval             255
Device Status:     0x0000
  (Bus Powered)
$ 

Eu não entendi e levanto duas questões de possibilidade:

1. Se o valor de bInterfaceProtocol sempre None independente de Host, então qual é o ponto dessa Interface não usada existir?
2. Se o valor de bInterfaceProtocol for decidido pelo Kernel, então o que é a condição que o Kernel levou para configurá-lo para None?