trace_irq_handler_exit — called immediately after the irq action handler returns
| void trace_irq_handler_exit ( | int irq, | 
| struct irqaction * action, | |
| int ret ); | 
   If the ret value is set to IRQ_HANDLED, then we know that the corresponding
   action->handler scuccessully handled this irq. Otherwise, the irq might be
   a shared irq line, or the irq was not handled successfully. Can be used in
   conjunction with the irq_handler_entry to understand irq handler latencies.