linux-kernel - Re: Threaded irq handler question

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Message-ID: <20100423132907.GB28132@sirena.org.uk>
Date:	Fri, 23 Apr 2010 14:29:07 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Will Newton <will.newton@...il.com>
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 05:35:32PM +0100, Will Newton wrote:

> 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:

...

> 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?

The genirq framework has native support for doing this using a oneshot
IRQ handler - if you request the IRQ with IRQF_ONESHOT and provide only 
a threaded IRQ handler then genirq will disable the interrupt when the
primary IRQ fires and schedule the threaded handler.

See wm831x or wm8350 for an example.
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