Date: Mon, 30 Nov 2009 15:01:00 +0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>,
       Rusty Russell <rusty@rustcorp.com.au>,
       David Brownell <dbrownell@users.sourceforge.net>,
       Eric Miao <eric.y.miao@gmail.com>,
       Andrea Gallo <andrea.gallo@stericsson.com>,
       Peter Zijlstra <peterz@infradead.org>,
       John Stultz <johnstul@us.ibm.com>, Nicolas Pitre <nico@marvell.com>,
       Jamie Lokier <jamie@shareable.org>, LKML <linux-kernel@vger.kernel.org>,
       Remy Bohmer <linux@bohmer.net>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
	<u.kleine-koenig@pengutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Ingo Molnar <mingo@elte.hu>, linux-arm-kernel@lists.infradead.org
Subject: Re: Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about
	IRQF_SHARED|IRQF_DISABLED)
Message-ID: <20091130150100.GB7028@n2100.arm.linux.org.uk>
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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.

Luckily, the timer interrupt is the first to claim, and so is the first
to be run.  However, there was a problem reported a while back of the
clock event code being called on AT91 with IRQs enabled - unfortunately
the original reporters stopped responding so it was never worked out
what was going on.

My point is that if we outlaw irqs-disabled shared interrupts, it puts
Atmel AT91 support into immediate difficulties.
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