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

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Message-ID: <20091130150100.GB7028@n2100.arm.linux.org.uk>
Date:	Mon, 30 Nov 2009 15:01:00 +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 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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