rw_lock vs mutex

[Paul Goyette <paul%whooppee.com@localhost>]

While digging around looking into another problem, I noticed that the 
piixpm(4) driver uses an rw_lock for its ic_acquire_bus/ic_release_bus 
routines.  ic_acquire_bus() uses rw_enter(..., RW_WRITER) and there 
doesn't appear to be any use anywhere of RW_READER for that lock.

The man page for rw_lock implies that it is a superset of a mutex.  So 
I'm wondering if it makes any sense to use the simpler mutex instead?


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