linux-kernel - Re: Threaded irq handler question

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Message-ID: <j2o87a5b0801004220351ze6948d6dn3d995122aff355b6@mail.gmail.com>
Date:	Thu, 22 Apr 2010 11:51:33 +0100
From:	Will Newton <will.newton@...il.com>
To:	Jonathan Corbet <corbet@....net>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Threaded irq handler question

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

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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