netdev - Re: [PATCH] netdev: enc28j60: use IRQF_TRIGGER

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Date:	Tue, 26 May 2009 12:40:16 -0700
From:	David Brownell <david-b@...bell.net>
To:	"Hennerich, Michael" <Michael.Hennerich@...log.com>
Cc:	"Baruch Siach" <baruch@...s.co.il>,
	"Mike Frysinger" <vapier@...too.org>, netdev@...r.kernel.org,
	"Bryan Wu" <cooloney@...nel.org>
Subject: Re: [PATCH] netdev: enc28j60: use IRQF_TRIGGER_FALLING for IRQ by default

On Tuesday 26 May 2009, Hennerich, Michael wrote:
> The comment block above request_irq states:
> 
> >> >     * level triggers won't currently work.
> 
> And I guess it's because IRQ handling is deferred to a work queue.

The IRQ needs to no longer be pending when the (hard) handler returns.
For level triggers, that means disabling the IRQ ... then re-enabling
it only when the (soft/threaded) handler returns.

> I wonder how IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING will work in
> such a case.

It works just fine, since when the (hard) handler returns there is
no longer "IRQ pending" status in the IRQ controller.

> Since the ENC28J60 /INT will de-assert during the work handler executes,
> thus causing a second spurious interrupt.

No problem.  The Ethernet adapter has no pending (unless another IRQ
triggered meanwhile); its workqueue/threaded handler returns immediately.

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