Re: This is where I'm going with fwcontrol

> send_phy_config() is causing the /dev/fwX device to generate a PHY 
> configuration Packet(IEEE 1394-1995 4.3.4.3)
> <snippet from document>
> It is possible to optimize Serial Bus performance for particular 
> configurations in the following ways:
>      a)   Setting the gap_count used by all nodes to a smaller value 
> (appropriate to the actual worst-case number of
>           hops between any two nodes)
>      b)   Forcing a particular node to be the root after the next bus 
> initialization (for example, in isochronous systems,
>           the root shall be cycle-master capable)
> Both of these actions shall be done for remote nodes using the PHY 
> configuration packet shown in figure 4.20. (For the
> local node, the PH_CONT.request service is used) The procedures for 
> using this PHY packet are described in clause
> 7.3.5.2.1.
> <end snippet>
> 
> So, I think you are correct adjust_gap_count should become set_root_node 
> as that is what it does.
> 
> A PHY Config packet should look like this:
> Message ID  Root ID  R T Gap Count
>    00(2 bits)  (5 bits)    1 1    (6 bits)
>  
> So the Root ID(-f in fwcontrol) can't be set to a value greater than 
> 0x3f(63) and the Gap Count can't be greater than 0x7f(127).  An "R" 
> value of 1 means that this is a message to set the root ID.  An "T" 
> value of 1 means that this is a message to set the gap count for all 
> nodes.  If "R" and "T" are both 0, then the message is ignored.

Thank you, this makes much more sense now!  I was looking at
controller registers, but it is building a packet.

Suggestion: put something like the text above in a comment
at the start of send_phy_config().
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