From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757140Ab0LHBAn (ORCPT ); Tue, 7 Dec 2010 20:00:43 -0500 Received: from kroah.org ([198.145.64.141]:48823 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757016Ab0LHBAh (ORCPT ); Tue, 7 Dec 2010 20:00:37 -0500 X-Mailbox-Line: From gregkh@clark.site Tue Dec 7 16:57:31 2010 Message-Id: <20101208005731.362628790@clark.site> User-Agent: quilt/0.48-11.2 Date: Tue, 07 Dec 2010 16:57:57 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Clemens Ladisch , Ingo Molnar , Thomas Gleixner , john stultz , Bob Picco Subject: [100/289] hpet: fix unwanted interrupt due to stale irq status bit In-Reply-To: <20101208005821.GA2922@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.36-stable review patch. If anyone has any objections, please let us know. ------------------ From: Clemens Ladisch commit 96e9694df446d1154ec2f4fdba8908588b9cba38 upstream. Jaswinder Singh Rajput wrote: > By executing Documentation/timers/hpet_example.c > > for polling, I requested for 3 iterations but it seems iteration work > for only 2 as first expired time is always very small. > > # ./hpet_example poll /dev/hpet 10 3 > -hpet: executing poll > hpet_poll: info.hi_flags 0x0 > hpet_poll: expired time = 0x13 > hpet_poll: revents = 0x1 > hpet_poll: data 0x1 > hpet_poll: expired time = 0x1868c > hpet_poll: revents = 0x1 > hpet_poll: data 0x1 > hpet_poll: expired time = 0x18645 > hpet_poll: revents = 0x1 > hpet_poll: data 0x1 Clearing the HPET interrupt enable bit disables interrupt generation but does not disable the timer, so the interrupt status bit will still be set when the timer elapses. If another interrupt arrives before the timer has been correctly programmed (due to some other device on the same interrupt line, or CONFIG_DEBUG_SHIRQ), this results in an extra unwanted interrupt event because the status bit is likely to be set from comparator matches that happened before the device was opened. Therefore, we have to ensure that the interrupt status bit is and stays cleared until we actually program the timer. Signed-off-by: Clemens Ladisch Reported-by: Jaswinder Singh Rajput Cc: Ingo Molnar Cc: Thomas Gleixner Cc: john stultz Cc: Bob Picco Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/char/hpet.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) --- a/drivers/char/hpet.c +++ b/drivers/char/hpet.c @@ -479,6 +479,21 @@ static int hpet_ioctl_ieon(struct hpet_d if (irq) { unsigned long irq_flags; + if (devp->hd_flags & HPET_SHARED_IRQ) { + /* + * To prevent the interrupt handler from seeing an + * unwanted interrupt status bit, program the timer + * so that it will not fire in the near future ... + */ + writel(readl(&timer->hpet_config) & ~Tn_TYPE_CNF_MASK, + &timer->hpet_config); + write_counter(read_counter(&hpet->hpet_mc), + &timer->hpet_compare); + /* ... and clear any left-over status. */ + isr = 1 << (devp - devp->hd_hpets->hp_dev); + writel(isr, &hpet->hpet_isr); + } + sprintf(devp->hd_name, "hpet%d", (int)(devp - hpetp->hp_dev)); irq_flags = devp->hd_flags & HPET_SHARED_IRQ ? IRQF_SHARED : IRQF_DISABLED;