linux-kernel - Re: Long playing threaded interrupt handlers

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Date:	Wed, 2 Jun 2010 09:19:21 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Long playing threaded interrupt handlers

On Wed, 2 Jun 2010, Dmitry Torokhov wrote:

> HI Thomas,
> 
> The threaded IRQ infrastructure that went into the kernel is extremely
> helpful, however in the input land there are quite a few devices that
> require polling after an IRQ has been raised.
> 
> Currently most such drivers, instead of threaded interrupts, still use
> [delayed] work to do the polling, and still face the issue of shutting
> down interrupt and scheduled work in a raceless way leaving irq enable
> counter balanced. Is it allowed to have threaded ISR execute for
> extended a amount of time, and do the required polling, provided that
> ISR does certain checks to finish promply in case when we unbind the
> driver or try to suspend the device?

Sure, why not ? The only thing we need to think about is when the poll
is busy polling for a long time, then we need to lower the irq thread
priority to SCHED_OTHER in order not to hog the CPU.

Vs. shutdown: The thread handler needs to be aware of a shutdown
request in it's poll loop, so something like this should work:

handler()
{
	while (work_to_do() && !shutdown) {
	      .....
	}
}

unbind()
{
	shutdown = 1;
	free_irq();
}

Thanks,

	tglx
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