What does 'usbconfig' output say? Does the output differ (for other things than bus and port number) if you run it with with the usb flash drive connected to the various ports?
AFAIK, the Pi2 (as the Pi1) only has one usb bus - everything hangs off that one.
FWIW, here is 'lsusb' output for my Pi2 (yeah, it runs Linux), please note that it also have an external hub connected (thus more than four ports): LibreELEC:~ # lsusb Bus 001 Device 007: ID 099a:6200 Zippy Technology Corp. Bus 001 Device 005: ID 0bc7:0004 X10 Wireless Technology, Inc. X10 Receiver Bus 001 Device 004: ID 04b4:6560 Cypress Semiconductor Corp. CY7C65640 USB-2.0 "TetraHub" Bus 001 Device 006: ID 062a:4105 Creative Labs Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. SMC9514 Hub Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
LibreELEC:~ # lsb_release -a LibreELEC (official) - Version: 7.0.2
I didn't try usbconfig, but I do have the boot messages. The relevent part is:
ugen0.4: at usbus0 umass0 on uhub1 umass0: on usbus0 (the SCSI subsystem is oblivious)
Next, I moved the USB flash drive to a different port on the RPI2. To my considerable surprise, it booted normally and seems to be running fine. Here's the corresponding part of the boot log:
ugen0.4: at usbus0 umass0 on uhub1 umass0: on usbus0 ugen0.5: at usbus0 da0 at umass-sim0 bus 0 scbus0 target 0 lun 0 da0: Fixed Direct Access SPC-4 SCSI device da0: Serial Number AA010804142156532241 da0: 40.000MB/s transfers da0: 30533MB (62533296 512 byte sectors) da0: quirks=0x2
This time the SCSI system woke up.
Then I went to a test machine and moved its USB flash to the same position as that which didn't work on the original machine. It, too, booted and ran as if nothing changes. Is there _any_ electrical difference between the USB ports, or are they all wired in parallel?
For now I'm stumped and relieved the troublesome host is running again.
For purposes of conversation it would, however, be convenient to have a naming convention. Right now the best I can do is say that the position which didn't work is upper left looking into the ports, the one which is presently working is upper right. Far as I can tell that's not indicated anywhere in the boot messages or usbconfig, such as usb0 or usb1. The unit number and address don't seem to change when the flash drive is moved.
If the problem stays gone, so much the better. If it comes back it would be really helpful to know how folks (and software) name the USB ports.
Just to forestall questions about faulty connections, I'll mention that booting an older kernel produced a normal startup, without touching any hardware. Thus, I don't think it was a bad connection.
That's my understanding also.
Clearly there's only one bus, but where do the device numbers come from?