Mechanism for consistent port ordering for TinyUSB CDC devices on Windows

[Qlexio]

I've got an ESP32-S3 + TinyUSB project that creates two CDC serial devices. On macOS and Linux these always enumerate in a consistent order, and thus I'm able to sort them trivially (e.g. on macOS /dev/cu.usbmodemmyproj1, /dev/cu.usbmodemmyproj3).

However, Windows does not do this and will sometimes reorder the COM numbers, such that the lower COM number may be the second port instantiated from TinyUSB. This is a problem as there seems to be no way with pyserial's list_ports method to determine the correct ordering of the ports. I've tried to sort by usb_info which includes the location, but location is only present on one of the two devices and it's not necessarily the first TinyUSB device. These are the two ports:

'USB VID:PID=303A:4002 SER=MYPROJ'
'USB VID:PID=303A:4002 SER=MYPROJ LOCATION=1-2.4.4:x.2'

I have a workaround using pywin32 that queries for serial devices, and then sorts by the MI_# string that's present in the PNPDeviceID (which consistently orders the ports correctly). This guarantees I can always pick the correct port even if the COM ordering is reversed.

def find_windows_com_ports(vid, pid, serial_number=None):
    import win32com.client

    # Caution: GPT says `Win32_SerialPort` isn't reliable with USB devices.
    # But using `Win32_PnPEntity` requires parsing the COM port out of the
    # `Name`` which seems like it might break on Chinese language systems.
    # Seems to work for me.
    wmi = win32com.client.GetObject("winmgmts:")
    query = f"SELECT * FROM Win32_SerialPort"
    serial_ports = []

    for device in wmi.ExecQuery(query):
        logger.info(f"Found COM port: {device.DeviceID} {device.PNPDeviceID}")
        if device.PNPDeviceID and f"VID_{vid}&PID_{pid}" in device.PNPDeviceID:
            com_port = device.DeviceID
            # Extract MI_ number from DeviceID
            # Not exactly sure what this is but it seems to consistently enumerate in a
            # consistent order for the two USB devices, regardless of the COM port order
            mi_match = re.search(r"MI_([0-9A-F]+)", device.PNPDeviceID)
            mi = mi_match.group(1) if mi_match else "Unknown"

            # If we had a way to get the "Bus reported device description" here that'd work too
            # and be more consistent with other platforms. But we don't, and I guess it's hard?
            # See also: https://github.com/pyserial/pyserial/pull/338
            if serial_number is not None:
                ports = list_ports.grep(com_port)
                port = next(ports)
                if port.serial_number != serial_number:
                    logger.info(f"Skipping {com_port} ({serial_number} != {port.serial_number})")
                    continue

            serial_ports.append((com_port, mi))

    # Sort by the second field (MI number)
    serial_ports.sort(key=lambda x: x[1])

    return [port[0] for port in serial_ports]

I don't love this workaround since it requires an additional dependency on Windows (pywin32) and is a special code path to maintain and test only for Windows.

I'm opening this issue to discuss other ways of capturing the device order in a way that can be exposed in serial.tools.list_ports. Exposing the MI_ number that pywin32 has could solve the problem. Or if we could get LOCATION included on both ports that would probably also solve the issue. Or possibly there's a more elegant solution I'm not informed enough to reason about!

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This issue has been cloned from: pyserial#767