Hi!
On 15:14 Thu 19 Jan , Ran Shalit wrote:
> Hello,
>
> I am trying to correctly register interrupt in kernel for user interface:
>
> irq handler
> =========
>
> static irqreturn_t irq_handler(int irq, void *dev_id)
> {
> struct elbit_irq_dev *elbit_irq = &elbit_irq_devices[0];
> printk("irq in\n");
>
> <<==== clear interrupt in fpga here or after the call to wake_up,
> (at the bottom of routine below ) ?
>
> atomic_set(&elbit_irq->flag, 1);
> wake_up_interruptible(&elbit_irq->pollw);
>
>
>
> return IRQ_HANDLED;
> }
>
> ioctl for waiting on interrupts
> ======================
>
> static long elbit_device_ioctl( struct file *filp, /* ditto */
> unsigned int ioctl_num, /* number and param for ioctl */
> unsigned long ioctl_param)
> {
> struct elbit_irq_dev *elbit_irq = &elbit_irq_devices[0];
>
> switch (ioctl_num) {
> case IOCTL_WAIT_IRQ:
> atomic_set(&elbit_irq->flag, 0);
> wait_event_interruptible(elbit_irq->pollw,
> atomic_read(&elbit_irq->flag) != 0) ;
> break;
>
>
> default:
> break;
> }
> return 0;
> }
>
> my questions:
> 1. does wake_up and wait_event are countable, i.e. if there are 2
> interrupts for example before wait_event is called, does it mean it
> wake_event will not sleep on 2 consecutive calls ?
No, wait_event will sleep if the test "atomic_read(&elbit_irq->flag) != 0"
says so. In your code there is a race condition:
1) interrupt handler sets flag to 1
2) ioctl sets it to 0
==> wait_event_interruptible sleeps even tough it probably should not
You may want to replace the atomic_set() with atomic_inc() and atomic_dec() if
you want to wake up once every time the interrupt handler gets executed.
> 2. should we put the clear of interrupts in fpga in the interrupt
> before or after the wake_up ?
I do not think that this makes any difference.
> can we put them instead in the userspace handler (IOCTL_WAIT_IRQ) instead
> of clearing the interrupt in the interrupt handler ?
I do not think that this will work.
-Michi
--
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.twilightparadox.com
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