USB Serial Port Assignment

Overview

The usbserial.c driver has been enhanced with a way to
explicitly assign serial ports to USB serial devices.

Before this enhancement, the ports were assigned based
on the order the USB serial devices were enumerated,
but this changed depending on when the devices were
plugged in, or how the system was booted.  Devices
like the EdgePort 4/s were particularly troublesome,
since they are really two two port devices and these
two devices were enumerated in different orders, randomly
changing the port assignments of the four ports on the
device.

The usbserial module now has a module parameter named
"reserve_ports".  This is an array of strings, one for
each USB serial port, beginning at /dev/ttyUSB0 and
continuing on up.  The string is a pattern that
reserves the port for a particular device by serial
number, by vendor/product id, or by device path.


Syntax

Initially the strings NULL for all ports, and these
NULL strings leave the port available for any device.

The first character of the string determines the type
of the pattern:

  S -- serial number
  V -- vendor/product id
  D -- device path
  ^ -- this port is available for a multiport device
       that matched the previous pattern
  - -- this port is not available for any device
  * -- this port is available for any device

The rest of the string is interpreted according to
the first character:

Serial Number
  The serial number is an ASCII string that is matched
  against the serial number reported by the device.  An
  "*" can be used at the beginning or end of this string
  as a wildcard to match the beginning or ending of any
  serial number.

Vendor/Product ID
  The vendor/product ids are two hex numbers separated by
  a ":" or "/".  Either number can be replaced by a "*"
  as a wildcard to match any vendor or product id.  The
  vendor and product ids should not have "0x" at the
  beginning.

Device Path
  The device path is a "/" separated path of decimal integers.
  The first integer is the bus number, the rest are the USB
  port numbers of sequence of hubs leading to the device.  Any
  integer in the path can be replaced by a "*" as a wildcard
  to match any port.

  For example, a device path like "D1/2/3" means the device
  attached to the 3rd port on the hub attached to the 2nd
  port on the virtual hub on bus 1.  When a device is attached
  the usb subsystem prints an informational message through
  syslog that gives the device path--be sure syslog is logging
  informational messages and look for the "new device connect"
  message to see the path.


Specifying the Module Parameters

The reserve_ports module parameter can be given on the insmod
or modprobe command line, or it can be given in the
/etc/modules.conf file, like this

  add options usbserial 'reserve_ports=V1608:242,S*-0,V1608:242,S*-1'


Examples

The three examples that follow all assign the first four USB serial
ports, /dev/ttyUSB0 through /dev/ttyUSB3, to an EdgePort 4/s.

  add options usbserial 'reserve_ports=SA32399053-0,^,SA32399053-1,^'

This example specifies the serial number of the device.  The
EdgePort 4/s looks like two different devices, one with a serial
number ending in "-0" for the first two ports and another with
serial number ending in "-1" for the second two serial ports.

  add options usbserial 'reserve_ports=D1/2/*/2,D1/2/*/2,D1/2/*/1,D1/2/*/1'

This example specifies the device path for an EdgePort 4s attached
to any port of a hub attached to the computer's 2nd USB port.  Since
the EdgePort 4/s looks like two devices behind a hub, the path to
the EdgePort 4/s shows one extra port; USB port 2 is used for the
first two ports, and USB port 1 is used for the second two ports.

  add options usbserial 'reserve_ports=V1608:242,S*-0,V1608:242,S*-1'

This example specifies the vendor and product id and the trailing
part of the serial number.  Since EdgePort 4/s looks like two
two port devices, the device with the first two ports must match 
two entries in the reserve_ports array; in this example that means
the the vendor id must be 0x1608, the product id must be 0x0242,
and the serial number must end in "-0".