From: Clemens Ladisch Date: Tue, 26 Oct 2010 21:22:13 +0000 (-0700) Subject: hpet: fix unwanted interrupt due to stale irq status bit X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=96e9694df446d1154ec2f4fdba8908588b9cba38;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git hpet: fix unwanted interrupt due to stale irq status bit 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 Signed-off-by: Linus Torvalds --- diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c index 84e6a7e673b7..a2cbb828e92a 100644 --- a/drivers/char/hpet.c +++ b/drivers/char/hpet.c @@ -465,6 +465,21 @@ static int hpet_ioctl_ieon(struct hpet_dev *devp) 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;