reset full-speed usb device number

Bug #1729890 reported by Sebastian Schauenburg on 2017-11-03
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
lcd4linux (Ubuntu)
Undecided
Unassigned

Bug Description

On Ubuntu MATE 17.10 (artful) I found this bug when I tried to get my DPF LCD screen (connected via USB) working. I also tested my Ubuntu 17.10 MATE laptop install and I get the same result, so it is not a hardware issue. On my Debian stretch laptop, it works just fine.

When I run 'lcd4linux -Fvvv' it fails with:
lcd4linux.c: initializing driver DPF
dpf_ax_open: found AX206 #1
dpf_ax_open: no matching USB device 'usb0' found!
dpf: cannot open dpf device usb0
Error initializing driver DPF: Exit!

meanwhile I can see the following in syslog:
Nov 3 16:40:31 prometheus kernel: [73114.705716] usb 3-12.2: reset full-speed USB device number 88 using xhci_hcd
Nov 3 16:40:31 prometheus kernel: [73114.835220] usb 3-12.2: USB disconnect, device number 88
Nov 3 16:40:31 prometheus kernel: [73114.929498] usb 3-12.2: new full-speed USB device number 89 using xhci_hcd
Nov 3 16:40:31 prometheus kernel: [73115.067057] usb 3-12.2: New USB device found, idVendor=1908, idProduct=0102
Nov 3 16:40:31 prometheus kernel: [73115.067061] usb 3-12.2: New USB device strings: Mfr=2, Product=3, SerialNumber=1
Nov 3 16:40:31 prometheus kernel: [73115.067062] usb 3-12.2: Product: USB-Display
Nov 3 16:40:31 prometheus kernel: [73115.067064] usb 3-12.2: Manufacturer: hackfin
Nov 3 16:40:31 prometheus kernel: [73115.067065] usb 3-12.2: SerialNumber: 002
Nov 3 16:40:31 prometheus mtp-probe: checking bus 3, device 89: "/sys/devices/pci0000:00/0000:00:14.0/usb3/3-12/3-12.2"
Nov 3 16:40:31 prometheus mtp-probe: bus: 3, device: 89 was not an MTP device

Somehow a USB reset is triggered, which disconnects and reconnects the LCD screen, which in turn causes the device not to be found, since the USB ID is incremented.

Apparently this happens when /tmp does not have exec. Remounting /tmp with exec provides a workaround.

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