Date: Sun, 1 Mar 2009 10:43:02 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: David Brownell <david-b@pacbell.net>
cc: Andrew Morton <akpm@linux-foundation.org>, me@felipebalbi.com,
       linux-kernel@vger.kernel.org, linux-input@vger.kernel.org,
       felipe.balbi@nokia.com, dmitry.torokhov@gmail.com, sameo@openedhand.com,
       a.p.zijlstra@chello.nl
Subject: Re: lockdep and threaded IRQs (was: ...)
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On Sat, 28 Feb 2009, David Brownell wrote:
> That seems to presume a hardirq-to-taskirq handoff.  But the
> problem case is taskirq-to-taskirq chaining, through e.g.
> what set_irq_chip_and_handler() provided.  (Details not very
> amenable to brief emails, just UTSL.)
> 
> Thing is, I'm not sure a per-IRQ thread can work easily with
> that chaining.  The chained IRQs can need to be handled before
> the top-level IRQ gets re-enabled.  That's why the twl4030-irq
> code uses just one taskirq thread for all incoming events.

This can be solved by a completion as well.
 
> (Which of course is rarely more than one at a time, so there's
> little reason not to share that task between the demuxing code
> and the events being demuxed.  Interrupts that need processing
> via I2C/SPI/etc are more or less by definition not frequent or
> performance-critical.)

Then all we need to provide in the generic code is a function which
does not go through the handle_IRQ_event() logic and calls the action
handler directly. Not rocket science to do that and better than using
a facility which is designed to run in hardirq context and expect that
it works in thread context without complaints.

Thanks,

	tglx
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