linux-kernel - Re: Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about IRQF_SHARED|IRQF

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Date:	Mon, 30 Nov 2009 15:43:29 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Eric Miao <eric.y.miao@...il.com>,
	Andrea Gallo <andrea.gallo@...ricsson.com>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <johnstul@...ibm.com>,
	Nicolas Pitre <nico@...vell.com>,
	Jamie Lokier <jamie@...reable.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Remy Bohmer <linux@...mer.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about
	IRQF_SHARED|IRQF_DISABLED)

On Mon, Nov 30, 2009 at 03:32:23PM +0000, Alan Cox wrote:
> On Mon, 30 Nov 2009 15:01:00 +0000
> Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> > On Mon, Nov 30, 2009 at 02:47:02PM +0000, Alan Cox wrote:
> > > SHARED|DISABLED ought to WARN_ON() and if that doesn't motivate people
> > > then return -EINVAL.
> > 
> > That is an impossibility.  There is hardware out there (AT91) where
> > the timer interrupt is shared with other peripherals, and you end
> > up with a mixture of irqs-disabled and irqs-enabled handlers sharing
> > the same interrupt.
> 
> Well that will encourage people to fix it.
> 
> > My point is that if we outlaw irqs-disabled shared interrupts, it puts
> > Atmel AT91 support into immediate difficulties.
> 
> If a driver disables the timer irq across a tick aren't you already in
> trouble ?

Not with this clockevents code - you can miss timer interrupts and the core
time keeping code catches up automatically.
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