linux kernel threaded irq

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1.How-to

request_threaded_irq()
{
action->handler = handler;
action->thread_fn = thread_fn;
->__setup_irq()
{
/*
* Create a handler thread when a thread function is supplied
* and the interrupt does not nest into another interrupt
* thread.
*/
if (new->thread_fn && !nested) {
struct task_struct *t;

t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
new->name);
adb shell ps -P -p
可以看到创建的irq thread:
USER PID PPID VSIZE RSS PRIO NICE RTPRI SCHED PCY WCHAN PC NAME
root 57 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/102-msm_iom
root 58 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/102-msm_iom
root 59 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/102-msm_iom
root 60 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/79-msm_iomm
root 61 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/78-msm_iomm
root 62 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/78-msm_iomm
root 63 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/74-msm_iomm
root 64 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/75-msm_iomm
root 65 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/75-msm_iomm
root 66 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/273-msm_iom
root 67 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/273-msm_iom
root 68 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/273-msm_iom
root 69 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/97-msm_iomm
root 70 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/97-msm_iomm
root 71 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/97-msm_iomm
root 77 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/402-mba
root 78 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/530-wcnss
root 134 2 0 0 -51 0 50 1 fg c0100ac8 00000000 S irq/335-main_tt

2.什么时候执行

产生中断之后先执行中断对应的hard handler,之后根据hard handler中断服务程序是否返回IRQ_WAKE_THREAD flag决定是否执行中断对应的thread_fn。
（下半部tasklet 也是在hard handler 中断服务程序中执行tasklet_schedule()触发的）
执行流程是下面这个样子的：
handle_irq_event_percpu()
->
trace_irq_handler_entry(irq, action);
res = action->handler(irq, action->dev_id);
trace_irq_handler_exit(irq, action, res);
->
switch (res) {
case IRQ_WAKE_THREAD:
/*
* Catch drivers which return WAKE_THREAD but
* did not set up a thread function
*/
if (unlikely(!action->thread_fn)) {
warn_no_thread(irq, action);
break;
}

irq_wake_thread(desc, action);

->static void irq_wake_thread(struct irq_desc *desc, struct irqaction *action)
{
wake_up_process(action->thread);

->
/*
* Interrupt handler thread
*/
static int irq_thread(void *data)
{
static const struct sched_param param = {
.sched_priority = MAX_USER_RT_PRIO/2,
};
sched_setscheduler(current, SCHED_FIFO, &param);//irq thread 优先级比ksoftirqd/N 高很多
->
ret = action->thread_fn(action->irq, action->dev_id);

3. 一个threaded irq 典型的例子

static int __devinit ads7846_probe(struct spi_device *spi)
{
err = request_threaded_irq(spi->irq, ads7846_hard_irq, ads7846_irq,
irq_flags, spi->dev.driver->name, ts);
这个驱动既申请了hard handler（ads7846_hard_irq）也申请了thread_fn（ads7846_irq）。

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