#885648 modemmanager: ModemManager interferes with Microchip's USB-to-Serial bridges by probing

Package:
modemmanager
Source:
modemmanager
Description:
D-Bus service for managing modems
Submitter:
"Jonas K."
Date:
2017-12-28 20:54:04 UTC
Severity:
normal
#885648#5
Date:
2017-12-28 20:50:37 UTC
From:
To:
ModemManager tries to detect serial modems by probing. This leads to unexpected behaviour of
Microchip's USB-to-Serial bridges (in this case MCP2200), which are mostly used in hobbyists'
projects. Probably a probing payload is sent which is accepted as input data by an
interfacing microcontroller.

ModemManager reports problems during probing via syslog:
 Dec 28 19:03:04 linux ModemManager[531]: <info>  Creating modem with plugin 'Generic' and '1' ports
 Dec 28 19:03:04 linux ModemManager[531]: <warn>  Could not grab port (tty/ttyACM0): 'Cannot add port 'tty/ttyACM0', unhandled serial type'
 Dec 28 19:03:04 linux ModemManager[531]: <warn>  Couldn't create modem for device at '/sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1': Failed to find primary AT port

Please update the Debian packages for stretch and sid to greylist such devices and prevent
further disturbance.


The file of interest is 'src/77-mm-usb-serial-adapters-greylist.rules' in the upstream project:
git://anongit.freedesktop.org/ModemManager/ModemManager
ssh://git.freedesktop.org/git/ModemManager/ModemManager
https://anongit.freedesktop.org/git/ModemManager/ModemManager.git

On line 15 to 16 it says:
 # Devices using Microchip's VID
 ATTRS{idVendor}=="04d8", ENV{ID_MM_DEVICE_MANUAL_SCAN_ONLY}="1"


This includes the MCP2200 which has:
VID: 04d8
PID: 00df


Best regards
Jonas K.