Distinguishing identical devices

[Mark Turner <turner@mc.com>]

We manufacture user-configurable multi-computer systems for
high performance applications.  Our PCI version may have many
copies of virtually identical compute node cards.  For several
reasons we need to know which card is which.  These reasons
might include the need to find an added-on I/O daughtercard, or
the need to know where the board is connected to a secondary
interconnect (which runs over the tops of the boards).

Is there a commonly used way to distinguish between identical 
PCI cards in the same system?  The techniques that have come to 
mind are:

  - Tell the driver software where each board lives in terms 
    of its bus#/device# on PCI.  This has some variability 
    depending on exactly how the system is configured, and 
    is not particularly user-friendly.

  - Place in config-space somewhere (or in VPD?) a unique
    identifier for each board, and have the driver software
    read and make sense of this.  We'd still need to indicate
    to the driver software something to relate what is read 
    to the system configuration as a whole.

I imagine that there are systems that have, say, multiple SCSI
controllers with disk chains off of them, or systems with 
multiple graphics systems (monitors) that need to be driven.  
How do these systems know which disk is which, or which screen
is which?  Do people use user-settable switches that can be
read by the driver software to distinguish devices?  Am I 
expected to go beyond the PCI interface to the device itself
to ask it for some self-identifying information that can help 
to distinguish it?  Any suggestions or related anecdotes would 
be welcome.

Thanks,

Mark Turner
Mercury Computer Systems
turner@mc.com