linux-kernel - Re: [PATCH] genirq: irq_chip->startup() usage in setup_irq and set_irq

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Date:	Tue, 26 Aug 2008 11:14:36 +0100
From:	Pawel MOLL <pawel.moll@...com>
To:	benh@...nel.crashing.org
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] genirq: irq_chip->startup() usage in setup_irq and
	set_irq_chained handler

> The second change is a significant semantic change. I wouldn't be
> surprised if I have cases that rely (or work around) the lack of
> startup() in set_irq_chained_handler(). I'll have to dbl check things
> next week. 

Let me briefly explain my situation. I have a main interrupt controller
which provides startup() and unmask/mask() functions. The first one is
rather expensive (as the controller itself is... hmmm...
complicated ;-), the second - very cheap. And that is how I understand
the different "levels" of interrupt access - startup() should be called
once, somewhere during request_irq(), (un)masking may be used
frequently.

And one of the interrupt is generated by hardware PIO controller. The
idea was obvious - register a chained handler, which decodes the PIO
controller state and generates a interrupt, which number may be obtained
by gpio_to_irq(). Sounds simple, doesn't it? :-)

And in that moment the problem raised its ugly head - the interrupt
controller's startup() was never called for the PIO interrupt (as there
was no request_irq()), so the hardware wasn't configured properly and...
well... bad things were happening ;-)

So unless I totally misunderstood the meaning of irq_chip callbacks, I
believe the startup() should be called in set_irq_chained_handler(). 

Regards

Paweł

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