Fix enumeration of USB devices without a short serial on Raspberry Pi 4

[andber1]

This will fix the issue with USB devices that do not have a short serial and are not listed when using serialport::available_ports(). serial_number is an optional field in the UsbPortInfo struct and is not required to be available.

In my specifc case I have the USB device "USB-Serial_Controller" from "Prolific_Technology_Inc." (vid: 0x067b, pid: 0x2303). When connected to a Raspberry 4 it is not shown. This pull request fixes this.

Related to #113

[sirhcel]

Thank you very much for your PR @andber1! It looks like the right thing to do here. We should not have detecting USB devices depending on optional properties.

[sirhcel]

I finally managed to set up a Raspberry Pi 4 to give this PR a check. I have no Prolific device at hand but a FTDI R2232 (without an external EEPROM and thereor) without a serial number. This device gets enumerated by the list_ports example just fine:

$ cargo run --example list_ports
[...]
Found 3 ports:
  /dev/ttyUSB1
    Type: USB
    VID:0403 PID:6010
     Serial Number:
      Manufacturer: FTDI
           Product: Dual RS232
[...]

I checked this with 18f5c2a. What do lsusb -v and udevadm info /dev/ttyUSBn report for the device in your case?

[andber1]

@sirhcel Unfortunately I do not have a Raspberry 4 to hand now. I put the Prolific controller in a Raspberry 3 and it got listed, because it is a USB device and not a PCI device as on the Raspberry 4. Here are the requested outputs. Perhaps it will still help.

$ lsusb -v
[...]
Bus 001 Device 004: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port / Mobile Phone Data Cable
Couldn't open device, some information will be missing
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               1.10
  bDeviceClass            0 
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x067b Prolific Technology, Inc.
  idProduct          0x2303 PL2303 Serial Port / Mobile Phone Data Cable
  bcdDevice            3.00
  iManufacturer           1 Prolific Technology Inc.
  iProduct                2 USB-Serial Controller
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x0027
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           3
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0 
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x000a  1x 10 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
[...]
$ udevadm info /dev/ttyUSB0
P: /devices/platform/soc/3f980000.usb/usb1/1-1/1-1:1.0/ttyUSB0/tty/ttyUSB0
M: ttyUSB0
R: 0
U: tty
D: c 188:0
N: ttyUSB0
L: 0
S: serial/by-path/platform-3f980000.usb-usb-0:1:1.0-port0
S: serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller-if00-port0
E: DEVPATH=/devices/platform/soc/3f980000.usb/usb1/1-1/1-1:1.0/ttyUSB0/tty/ttyUSB0
E: DEVNAME=/dev/ttyUSB0
E: MAJOR=188
E: MINOR=0
E: SUBSYSTEM=tty
E: USEC_INITIALIZED=561403310
E: ID_BUS=usb
E: ID_MODEL=USB-Serial_Controller
E: ID_MODEL_ENC=USB-Serial\x20Controller
E: ID_MODEL_ID=2303
E: ID_SERIAL=Prolific_Technology_Inc._USB-Serial_Controller
E: ID_VENDOR=Prolific_Technology_Inc.
E: ID_VENDOR_ENC=Prolific\x20Technology\x20Inc.
E: ID_VENDOR_ID=067b
E: ID_REVISION=0300
E: ID_TYPE=generic
E: ID_USB_MODEL=USB-Serial_Controller
E: ID_USB_MODEL_ENC=USB-Serial\x20Controller
E: ID_USB_MODEL_ID=2303
E: ID_USB_SERIAL=Prolific_Technology_Inc._USB-Serial_Controller
E: ID_USB_VENDOR=Prolific_Technology_Inc.
E: ID_USB_VENDOR_ENC=Prolific\x20Technology\x20Inc.
E: ID_USB_VENDOR_ID=067b
E: ID_USB_REVISION=0300
E: ID_USB_TYPE=generic
E: ID_USB_INTERFACES=:ff0000:
E: ID_USB_INTERFACE_NUM=00
E: ID_USB_DRIVER=pl2303
E: ID_VENDOR_FROM_DATABASE=Prolific Technology, Inc.
E: ID_MODEL_FROM_DATABASE=PL2303 Serial Port / Mobile Phone Data Cable
E: ID_PATH=platform-3f980000.usb-usb-0:1:1.0
E: ID_PATH_TAG=platform-3f980000_usb-usb-0_1_1_0
E: ID_MM_CANDIDATE=1
E: DEVLINKS=/dev/serial/by-path/platform-3f980000.usb-usb-0:1:1.0-port0 /dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller-if00-port0
E: TAGS=:systemd:
E: CURRENT_TAGS=:systemd:

[sirhcel]

Thank you very much for for looking up the device information @andber1! The device descriptor does not look special, udev reports in as a USB device and therefor ID_USB_SERIAL_SHORT does not matter.

I finally got a Prolific PL2303 device into my hands today and - well - it enumerate just fine in my setup:

$ cargo run --example list_ports
[...]
Found 2 ports:
  /dev/ttyUSB1
    Type: USB
    VID:067b PID:2303
     Serial Number:
      Manufacturer: Prolific Technology Inc.
           Product: USB-Serial Controller D
[...]

Now I see what I missed in #160 (comment) and what happens here as well: The device is actually reported as an USB device. 🤦

I also found device information seen on a Raspberry Pi 4 back in 2023 in #110 (comment). Looks like libudev changed how these devices are reported in my setup.

Nevertheless, your proposed changes are the right thing to do for older/different setups with a Raspberry Pi 4.