Re: Threaded irq handler question

[Will Newton]

On Wed, Apr 21, 2010 at 6:28 PM, Jonathan Corbet <corbet@xxxxxxx> wrote:
> On Wed, 21 Apr 2010 17:35:32 +0100
> Will Newton <will.newton@xxxxxxxxx> 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.

Unfortunately this device has no way of doing that - deasserting the
interrupt line involves doing i2c transactions which will likely sleep
so cannot be done in the check handler. This is quite a common problem
for i2c connected devices.
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