>There may be more than one "soft interrupt" level ...

But there may not, and (as on the i386) soft interrupts might even
have to be handled entirely in software (in which case you could,
of course, have an arbitrary number of softint levels, depending on
how much work you wanted to do in the spl functions).

Exactly what sort of argument this forms, if any, is not really clear.

>... so this MI interface could not replace the currently MD facilities
>in the sun3 or sparc ports

The zs hard/soft interrupt split is machine-dependent anyway: on
the DECstation, there would be no reason to make such a split.
The same argument may apply to audio interrupts as well.

>#define SOFTINT_NET     1       /* old setsoftnet() */
>#define SOFTINT_CLOCK   1       /* old setsoftclock() */

These have always been the same priority, and there is no real reason
not to collapse them into one level.

Chris