I was having problems with mbed-tools detect even though mbed detect seems to work just fine. Using mbed-tools detect resulted in a trace dump culminating in this error:
mbed_tools.devices._internal.candidate_device.USBDescriptorError: serial_number cannot be an empty field and must be a string.
I looked into it a bit traced the problem to mbed_tools/devices/_internal/linux/device_detector.py. Specifically, within LinuxDeviceDetector, the find_candidates() code wasn’t always getting a text serial number where it expected one. I added a line if isinstance(serial_number, str): just above the try/except block and now it works just fine. It was apparently getting to that line twice, maybe once for the serial port and once for the drive on the same physical device? I don’t know, but it’s now working for me.
I’m running on Fedora 34 with a 64-bit machine and I am using Mbed CLI 2 with the latest ST driver installed and configured.