request_irq.txt

// Linux interrupt handler
// request_irq()
// Linux 4.9

// setup handler to irqaction
- request_threaded_irq()
  
  - source: include/linux/interrupt.h, kernel/irq/manage.c
  - irqaction is a chain(queue?) in irq_desc
  - if IRQF_SHARED isn't set, there is only one irqaction in the chain.

  // details
  request_irq()
  - request_threaded_irq(): action->handler = handler
  - __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
    
      irqaction** old_ptr = &desc->action;
      // set old_ptr to end of irqaction chain (action->next)
      *old_ptr = new; 
      irq_pm_install_action(desc, new); => desc->nr_actions++:

// interrupt handling by irq_desc's irqaction's handler
- handle_simple_irq()

  - call desc->action->handler() 
  - alternatives: handle_level_irq(), handle_edge_irq(), handle_fasteoi_irq(), handle_edge_eoi_irq()
  - source: kernel/irq/chip.c, kernel/irq/handle.c

  // details
  void handle_simple_irq(struct irq_desc *desc) 
  => irqreturn_t handle_irq_event(struct irq_desc *desc) 
  => irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
  => irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc, unsigned int *flags) 
  => action->handler(irq, action->dev_id);

// misc
// 1. irq thread: irqaction->{thread, thread_fn}, kthread_create() at setup_irq_thread()
// 2. irq domain remapping: kernel/irq/irqdomain.c