rtc-cmos: avoid spurious irqs

This fixes kernel http://bugzilla.kernel.org/show_bug.cgi?id=11112 (bogus
RTC update IRQs reported) for rtc-cmos, in two ways:

  - When HPET is stealing the IRQs, use the first IRQ to grab
    the seconds counter which will be monitored (instead of
    using whatever was previously in that memory);

  - In sane IRQ handling modes, scrub out old IRQ status before
    enabling IRQs.

That latter is done by tightening up IRQ handling for rtc-cmos everywhere,
also ensuring that when HPET is used it's the only thing triggering IRQ
reports to userspace; net object shrink.

Also fix a bogus HPET message related to its RTC emulation.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Report-by: W Unruh <unruh@physics.ubc.ca>
Cc: Andrew Victor <avictor.za@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 0ea6a19bfdfe..ad2b15a1334d 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -468,7 +468,7 @@ void hpet_disable(void)
 #define RTC_NUM_INTS            1
 
 static unsigned long hpet_rtc_flags;
-static unsigned long hpet_prev_update_sec;
+static int hpet_prev_update_sec;
 static struct rtc_time hpet_alarm_time;
 static unsigned long hpet_pie_count;
 static unsigned long hpet_t1_cmp;
@@ -575,6 +575,9 @@ int hpet_set_rtc_irq_bit(unsigned long bit_mask)
 
         hpet_rtc_flags |= bit_mask;
 
+        if ((bit_mask & RTC_UIE) && !(oldbits & RTC_UIE))
+                hpet_prev_update_sec = -1;
+
         if (!oldbits)
                 hpet_rtc_timer_init();
 
@@ -652,7 +655,7 @@ static void hpet_rtc_timer_reinit(void)
                 if (hpet_rtc_flags & RTC_PIE)
                         hpet_pie_count += lost_ints;
                 if (printk_ratelimit())
-                        printk(KERN_WARNING "rtc: lost %d interrupts\n",
+                        printk(KERN_WARNING "hpet1: lost %d rtc interrupts\n",
                                 lost_ints);
         }
 }
@@ -670,7 +673,8 @@ irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
 
         if (hpet_rtc_flags & RTC_UIE &&
             curr_time.tm_sec != hpet_prev_update_sec) {
-                rtc_int_flag = RTC_UF;
+                if (hpet_prev_update_sec >= 0)
+                        rtc_int_flag = RTC_UF;
                 hpet_prev_update_sec = curr_time.tm_sec;
         }