Debian discussion to disable automatic TTY probing

[Bjørn Mork]

Aleksander Morgado <aleksander at aleksander.es> writes:

> Hey!
>
> FYI
>
> Got told today that Debian is discussing whether to disable automatic
> probing of TTY devices in MM, some links:
>
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=877024
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=683839
>
> This is the ModemManager bug report about this issue, for reference:
> https://bugs.freedesktop.org/show_bug.cgi?id=85007


Thanks for pointing to these. Just one data point regarding the question
you ask:

  "We have more than one TTY exposed by the same USB device (are there
  non-modem devices out there that would usually do this?)."

Yes, there are such devices.  Most multiport USB serial devices fall
into this group.  I have this one for example:

root at wrt1900ac-1:~# lsusb -vd 1608:0001

Bus 002 Device 002: ID 1608:0001 Inside Out Networks [hex] EdgePort/4 Serial Port
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               1.00
  bDeviceClass          255 Vendor Specific Class
  bDeviceSubClass         0 
  bDeviceProtocol       255 
  bMaxPacketSize0         8
  idVendor           0x1608 Inside Out Networks [hex]
  idProduct          0x0001 EdgePort/4 Serial Port
  bcdDevice            1.00
  iManufacturer           1 Inside Out Networks
  iProduct                2 Edgeport/4
  iSerial                 5 V13408648
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           39
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          3 Configuration #1Conf
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower              140mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           3
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0 
      bInterfaceProtocol    255 
      iInterface              4 Interface #1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0020  1x 32 bytes
        bInterval               2
Device Status:     0x0000
  (Bus Powered)

root at wrt1900ac-1:~# ls -l /sys/bus/usb-serial/devices/
lrwxrwxrwx    1 root     root             0 Sep 28 19:05 ttyUSB0 -> ../../../devices/platform/soc/soc:pcie-controller/pci0000:00/0000:00:01.0/0000:01:00.0/usb2/2-2/2-2:1.0/ttyUSB0
lrwxrwxrwx    1 root     root             0 Sep 28 19:05 ttyUSB1 -> ../../../devices/platform/soc/soc:pcie-controller/pci0000:00/0000:00:01.0/0000:01:00.0/usb2/2-2/2-2:1.0/ttyUSB1
lrwxrwxrwx    1 root     root             0 Sep 28 19:05 ttyUSB2 -> ../../../devices/platform/soc/soc:pcie-controller/pci0000:00/0000:00:01.0/0000:01:00.0/usb2/2-2/2-2:1.0/ttyUSB2
lrwxrwxrwx    1 root     root             0 Sep 28 19:05 ttyUSB3 -> ../../../devices/platform/soc/soc:pcie-controller/pci0000:00/0000:00:01.0/0000:01:00.0/usb2/2-2/2-2:1.0/ttyUSB3


Your other rule looks good though.  I cannot think of any composite
net+serial device which isn't a modem.  And that should catch all newer
modems, shouldn't it? 


Bjørn