linux-kernel - Re: [PATCH/RFC] hardware irq debouncing support

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Date:	Mon, 6 Oct 2008 17:10:03 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	David Brownell <david-b@...bell.net>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	Andrew Victor <linux@...im.org.za>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH/RFC] hardware irq debouncing support

On Wed 2008-09-24 12:51:32, David Brownell wrote:
> Hardware IRQ debouncing is common for IRQ controllers which are
> part of GPIO modules ... they often deal with mechanical switches,
> buttons, and so forth.  This patch:
> 
>  - Provides simple support for that in genirq
> 
>  - Includes sample implementations for some Linux systems
>    which already include non-generic support for this:
> 
>      * Atmel SOCs (AT91, AT32 -- the same GPIO module)
>      * OMAP2/OMAP3 (not quite as simple)
> 
> Control over how long to debounce is less common, and often applies
> to banks of GPIOs not individual signals ... not addressed here.
> 
> Drivers can request this (where available) with a new IRQF_DEBOUNCED
> flag/hint passed to request_irq():
> 
>     IF that flag is set when a handler is registered
> 	AND the relevant irq_chip supports debouncing
> 	AND the IRQ isn't already flagged as being debounced
>     THEN the irq_chip is asked to enable debouncing for this IRQ
> 	UNTIL the IRQ's last handler is unregistered.
>     ELSE
>         nothing is done ... the hint is ignored
>     FI
> 
> Comments?

How is this going to work with shared interrupt lines? If one handler
wants debouncing and second handler does not, you'll loose interrupts
for second handler?

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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