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.
4Calls 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).
5Releases the simple lock and resets the IPL.
6Calls the splx( ) routine to reset the CPU priority to the level that is stored in the s variable.
