From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: + hpet-fix-unwanted-interrupt-due-to-stale-irq-status-bit.patch added to -mm tree Date: Tue, 07 Sep 2010 13:00:41 -0700 Message-ID: <201009072000.o87K0fVR002725@imap1.linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:43827 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758181Ab0IGUJI (ORCPT ); Tue, 7 Sep 2010 16:09:08 -0400 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: mm-commits@vger.kernel.org Cc: clemens@ladisch.de, bpicco@redhat.com, jaswinderlinux@gmail.com, johnstul@us.ibm.com, mingo@elte.hu, stable@kernel.org, tglx@linutronix.de The patch titled hpet: fix unwanted interrupt due to stale irq status bit has been added to the -mm tree. Its filename is hpet-fix-unwanted-interrupt-due-to-stale-irq-status-bit.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: hpet: fix unwanted interrupt due to stale irq status bit From: Clemens Ladisch 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 Cc: Signed-off-by: Andrew Morton --- drivers/char/hpet.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff -puN drivers/char/hpet.c~hpet-fix-unwanted-interrupt-due-to-stale-irq-status-bit drivers/char/hpet.c --- a/drivers/char/hpet.c~hpet-fix-unwanted-interrupt-due-to-stale-irq-status-bit +++ a/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; _ Patches currently in -mm which might be from clemens@ladisch.de are linux-next.patch hpet-unmap-unused-i-o-space.patch hpet-fix-unwanted-interrupt-due-to-stale-irq-status-bit.patch hpet-factor-timer-allocate-from-open.patch