Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752387AbaAXKz6 (ORCPT ); Fri, 24 Jan 2014 05:55:58 -0500 Received: from gw-1.arm.linux.org.uk ([78.32.30.217]:47132 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752064AbaAXKz4 (ORCPT ); Fri, 24 Jan 2014 05:55:56 -0500 Date: Fri, 24 Jan 2014 10:55:39 +0000 From: Russell King - ARM Linux To: Jason Gunthorpe Cc: Sebastian Hesselbarth , Andrew Lunn , Jason Cooper , linux-kernel@vger.kernel.org, Ezequiel Garcia , Gregory Clement , Thomas Gleixner , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 3/3] irqchip: orion: clear stale interrupts in irq_enable Message-ID: <20140124105539.GD15937@n2100.arm.linux.org.uk> References: <1390516686-2224-1-git-send-email-sebastian.hesselbarth@gmail.com> <1390516686-2224-4-git-send-email-sebastian.hesselbarth@gmail.com> <20140123225208.GA24778@obsidianresearch.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140123225208.GA24778@obsidianresearch.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 23, 2014 at 03:52:08PM -0700, Jason Gunthorpe wrote: > On Thu, Jan 23, 2014 at 11:38:06PM +0100, Sebastian Hesselbarth wrote: > > Bridge IRQ_CAUSE bits are asserted regardless of the corresponding bit in > > IRQ_MASK register. To avoid interrupt events on stale irqs, we have to clear > > them before unmask. This installs an .irq_enable callback to ensure stale > > irqs are cleared before initial unmask. > > I'm not sure if putting this in irq_enable is correct. I think this > should only happen at irq_startup. > > The question boils down to what is supposed to happen with this code > sequence: > > disable_irq(..); > write(.. something to cause an interrupt edge ..); > .. synchronize .. > enable_irq(..); > > Do we get the interrupt or not? The answer is... yes, the interrupt should be delivered after the interrupt is re-enabled. > I found this message from Linus long ago: > http://yarchive.net/comp/linux/edge_triggered_interrupts.html > > Btw, the "disable_irq()/enable_irq()" subsystem has been written so that > > when you disable an edge-triggered interrupt, and the edge happens while > > the interrupt is disabled, we will re-play the interrupt at enable time. > > Exactly so that drivers can have an easier time and don't have to > > normally worry about whether something is edge or level-triggered. > > And found this note in Documentation/DocBook/genericirq.tmpl: > > > This prevents losing edge interrupts on hardware which does > > not store an edge interrupt event while the interrupt is disabled at > > the hardware level. > > So I think it is very clear that the chip driver should not discard > edges that happened while the interrupt was disabled. Correct. -- FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up. Estimation in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad. Estimate before purchase was "up to 13.2Mbit". -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/