Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754625Ab0LLXqE (ORCPT ); Sun, 12 Dec 2010 18:46:04 -0500 Received: from one.firstfloor.org ([213.235.205.2]:44910 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754604Ab0LLXp7 (ORCPT ); Sun, 12 Dec 2010 18:45:59 -0500 From: Andi Kleen References: <201012131244.547034648@firstfloor.org> In-Reply-To: <201012131244.547034648@firstfloor.org> To: clemens@ladisch.de, mingo@elte.hu, tglx@linutronix.de, johnstul@us.ibm.com, bpicco@redhat.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, gregkh@suse.de, ak@linux.intel.com, linux-kernel@vger.kernel.org, stable@kernel.org Subject: [PATCH] [60/223] hpet: fix unwanted interrupt due to stale irq status bit Message-Id: <20101212234558.24FDBB27BF@basil.firstfloor.org> Date: Mon, 13 Dec 2010 00:45:58 +0100 (CET) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3133 Lines: 83 2.6.35-longterm review patch. If anyone has any objections, please let me 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 Signed-off-by: Andi Kleen --- drivers/char/hpet.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) Index: linux/drivers/char/hpet.c =================================================================== --- linux.orig/drivers/char/hpet.c +++ linux/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; -- 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/