linux-kernel - Re: genirq: Add a set_irq_handler

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Message-ID: <20070212093549.GA22465@flint.arm.linux.org.uk>
Date:	Mon, 12 Feb 2007 09:35:49 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	David Gibson <david@...son.dropbear.id.au>,
	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 Mon, Feb 12, 2007 at 02:17:28PM +1100, David Gibson wrote:
> 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.

Do you have a better way of naming the functions?

> 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.

If you have correct behaviour from your interrupt controller for edge
based interrupts, you don't need the lazy masking, so why make things
complicated in this way?

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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