From: Will Newton on
Hi all,

I have a threaded irq handler attached to a level-triggered gpio
interrupt line. The check handler checks the status of the gpio line
and disables the irq line amd returns WAKE_THREAD in that case:

static irqreturn_t isr_check(int irq, void *p)
{
if (gpio_status()) {
disable_irq_nosync(irq);
return IRQ_WAKE_THREAD;
}

return IRQ_NONE;
}

The thread then does some i2c transactions that will eventually
deassert the gpio line:

static irqreturn_t isr(int irq, void *p)
{
/* do some i2c transfers */
enable_irq(irq);
return IRQ_HANDLED;
}

My problem is that this structure does not work, because once I call
disable_irq_nosync() on the irq in the check handler the thread will
no longer run because the irq is disabled. However if I don't call
disable_irq_nosync() I will get endless irqs because the line is
level-triggered and will not be deasserted until the thread has run.

Could someone tell me what I'm doing wrong here?

Thanks,
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From: Jonathan Corbet on
On Wed, 21 Apr 2010 17:35:32 +0100
Will Newton <will.newton(a)gmail.com> wrote:

> My problem is that this structure does not work, because once I call
> disable_irq_nosync() on the irq in the check handler the thread will
> no longer run because the irq is disabled. However if I don't call
> disable_irq_nosync() I will get endless irqs because the line is
> level-triggered and will not be deasserted until the thread has run.

Trying to disable IRQs at this level is the wrong approach. You need to
do enough in the primary interrupt handler to cause the hardware to
stop interrupting in the first place; usually that's just a matter of
some sort of acknowledgment. Then the threaded handler can move data
around in peace.

jon
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From: Yong Zhang on
On Wed, Apr 21, 2010 at 05:35:32PM +0100, Will Newton wrote:
> Hi all,
> My problem is that this structure does not work, because once I call
> disable_irq_nosync() on the irq in the check handler the thread will
> no longer run because the irq is disabled. However if I don't call
> disable_irq_nosync() I will get endless irqs because the line is
> level-triggered and will not be deasserted until the thread has run.
>
> Could someone tell me what I'm doing wrong here?

Does IRQF_ONESHOT meet your need?

Thanks,
Yong
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