linux-kernel - Re: [PATCH] Support IRQ_NOAUTOEN flag in set_irq_chained

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Date:	Tue, 22 Mar 2011 12:17:20 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Esben Haabendal <eha@....doredevelopment.dk>
cc:	Esben Haabendal <eha@...edevelopment.dk>,
	linux-kernel@...r.kernel.org, grant.likely@...retlab.ca
Subject: Re: [PATCH] Support IRQ_NOAUTOEN flag in set_irq_chained_handler()

On Tue, 22 Mar 2011, Esben Haabendal wrote:

> Thomas Gleixner <tglx@...utronix.de> writes:
> 
> > On Fri, 18 Mar 2011, eha@...edevelopment.dk wrote:
> >
> >> From: Esben Haabendal <eha@...edevelopment.dk>
> >> 
> >> Handle IRQ_NOAUTOEN in __set_irq_handler() (ie. for
> >> set_irq_chained_handler()) instead of just silently ignoring it, and in
> >> the same way as is done in __setup_irq() (ie. request_irq()).
> >> 
> >> This give a more consistent interface, and also adheres better to
> >> the rule of least surprise.
> >
> > Well, that might be less surprising for you, but you will be surprised
> > that such a change would be a real big surprise for all users of
> > chained handlers in arch/arm. They simply would not work anymore.
> 
> How is that?  I don't see any use of IRQ_NOAUTOEN flag in arch/arm at
> all.  Is there some other way that IRQ_NOAUTOEN get's enabled in
> arch/arm?  Or is my patch broken in some way that it does change irq
> handler setup when IRQ_NOAUTOEN is not set?

Ooops, sorry. I had it somewhere in the back of my memory that ARM
marked all interrupts IRQ_NOAUTOEN by default. Confused that with
NOPROBE.
 
> The idea of the patch is that it will do exactly the same as
> before, unless you specifically set IRQ_NOAUTOEN before calling
> set_irq_chained_handler...

I understand the patch :)
 
> > So we _cannot_ change the semantics here. All we can do is document
> > it.
> 
> With the current semantics, how are one supposed to be able use
> set_irq_chained_handler without having the handler enabled immediately?

Not at all. Why do you want to do that ?

Thanks,

	tglx
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