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

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Message-Id: <1219795619.13162.166.camel@pasglop>
Date:	Wed, 27 Aug 2008 10:06:59 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Pawel MOLL <pawel.moll@...com>
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

On Tue, 2008-08-26 at 11:14 +0100, Pawel MOLL wrote:

> 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.

Oh, I don't disagree. It's probably a good idea. I'm just worried of
the potential impact on existing code written around the current
behaviour.

We have 23 calls to set_irq_chained_handler in arch/powerpc, and I need
to audit them all. Luckily, we mostly don't have startup() callbacks.

 (... some time later ...)

It looks good. Of course, we'll have to test at one point, but at this
stage, I think powerpc is happy with the change.

Interestingly enough, I can see a case where we would have a problem
-without- your change :-) Not with the current code, but in conjunction
with another change that's planned for .28.

So Acked-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>

Cheers,
Ben.




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