Compaq TRU64 AA-RNG2A-TE - Manual (Page 84)

Because simple locks are spin locks, simple_lock( ) does not return
until the lock has been obtained.
The el_softc_lock member of the el_softc data structure points to
a simple lock data structure. The if_el device driver declares this data
structure by calling the decl_simple_lock_data( ) routine.
4 Calls the WRITE_CMD macro to write data to the command port register.
In this call, el_autosense_thread( ) passes the if_el driver’s
el_softc
data structure pointer. The data to be written is the statistics
disable command (CMD_STATDIS).
5 Releases the simple lock and resets the IPL.
6 Calls the splx( ) routine to reset the CPU priority to the level that is
stored in the s variable.
5–26 Implementing the Autoconfiguration Support Section (probe)