linux-kernel - Re: genirq: Add a set_irq_handler

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Date:	Mon, 12 Feb 2007 14:17:28 +1100
From:	David Gibson <david@...son.dropbear.id.au>
To:	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: genirq: Add a set_irq_handler_locked() function

On Fri, Feb 09, 2007 at 07:36:40AM +0000, Russell King wrote:
> On Fri, Feb 09, 2007 at 02:48:42PM +1100, David Gibson wrote:
> > At present set_irq_handler() and all the existing variants take the
> > desc->lock for the irq in question before adjusting the irq's flow
> > handler.  This can cause problems for irq chips for which a given
> > interrupt can be either level or edge depending on what's attached.
> 
> Are you sure you need to change the flow handler depending on how
> you program the device?
> 
> Since the outset of this design, I've had what are essentially edge
> based interrupt sources using the "level" handlers because they haven't
> had a "broken" edge implementation.  By that, I mean that the masking
> is done in such a way that you miss edges when the source is masked.
> 
> If you do not miss edges while the source is masked, there's no point
> in having the complexity of the "edge" based handler in the path - it
> buys you nothing.  Just use the "level" handler instead.

I see... how terribly obvious.

As far as I know, the 4xx UIC does things correctly, though I don't
have handy any devices with edge interrupts to test it with.

It would still be nice to have this change, so we can use the
lazy-masking from handle_edge_irq(), but I guess I can do without it
for now.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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