int pm_send (struct pm_dev * dev, pm_request_t rqst, void * data);
Issue a power management request to a given device. The PM_SUSPEND and PM_RESUME events are handled specially. The data field must hold the intended next state. No call is made if the state matches.
what stops two power management requests occurring in parallel and conflicting.
Calling pm_send directly is not generally recommended, in particular there is no locking against the pm_dev going away. The caller must maintain all needed locking or have 'inside knowledge' on the safety. Also remember that this function is not locked against pm_unregister. This means that you must handle SMP races on callback execution and unload yourself.