>Aha - that is what it was good for.

The thing that led me originally to "cd_aux" was the old Unibus
configuration code, in which each Unibus driver had, in addition
to the configuration-line address, a set of "standard" addresses.
I figured the uba driver code would look something very vaguely
like (most types and such left out):

	ubaattach(parent, self, aux)
		...
		config_search(ubaprobe, self, &probedata);


	ubaprobe(parent, cf, aux0) {
		struct ubaaux *aux = aux0;
		struct cfdriver *cd;
		struct uba_cfdriver *ud;
		u_short *sp;
		int found = 0;

		cd = cf->cf_driver;
		ud = cd->cd_aux;

		... (the usual setup code) ...

		/* first ask about the configured address --
		   note, we (a) do not use the cd_match function,
		   and/or (b) stick the address in aux, and/or (c)
		   fiddle with cf->cf_loc[]; (a) + (b) shown here
		   ((c) is generally Evil, (b) alone is probably
		   best, but hey, this is just an example! :-) ). */
		aux->addr = cf->cf_loc[0];
		if (ud->ud_probe(parent, cf, aux) &&
		    (!is_dw780(uba) || !dw780_err(uba)))
			found = 1;

		/* now ask about "std" addresses as defined by driver */
		for (sp = ud->ud_stdaddr; !found && *sp; sp++) {
			aux->addr = *sp;
			if (ud->ud_probe(parent, cf, aux) &&
			    (!is_dw780(uba) || !dw780_err(uba)))
				found = 1;
		}
		if (found)
			config_attach(parent, cf, aux, ubaprint);
		return 0;	/* always continue probing */
	}

That this means anything that configures "at uba" has to provide
a "uba_cfdriver" as its cd_aux.  So, to make a driver that could
be "at uba" and also (for a bad example) "at sbus", the cd_aux
field has to be attachment-specific.  (BSD/OS does not yet have
the attachment-specific match/attach stuff from NetBSD.)

Chris