On a low end box with tight IRQ timing they buy you a lot. There are reasons
MacOS does better than Linux on m68k serial performance. On modern machines
and things like the PC what you say is very true but not on old m68k boxen
However there are much cleaner ways to attack this.
Add an arch specific
spin_lockat_cli(lock, flags, pri)
and make the normal cli() raise your IPL to screen all but what are effectively
the 'real time' irqs. You don't want to do this in the generic driver case
or for most platforms but used in the m68k serial drivers its pretty much
essential - as on the mac it is for localtalk
Alan
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