Man page 9 : wait_for_completion_timeout

wait_for_completion_timeout - waits for completion of a task (w/timeout)

unsigned long __sched wait_for_completion_timeout(struct completion *  x , unsigned long  timeout );

x
    holds the state of this particular completion

timeout
    timeout value in jiffies

This waits for either a completion of a specific task to be signaled or for a specified timeout to expire. The timeout is in jiffies. It is not interruptible.

The return value is 0 if timed out, and positive (at least 1, or number of jiffies left till timeout) if completed.