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

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Date:	Tue, 22 Mar 2011 10:05:11 +0100
From:	Esben Haabendal <eha@....doredevelopment.dk>
To:	Thomas Gleixner <tglx@...utronix.de>
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()

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?

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...

> 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?

/Esben
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