rtc-cmos alarm acts as oneshot

Start making the rtc-cmos alarm act more like a oneshot alarm by disabling
that alarm after its IRQ fires.  (ACPI hooks are also needed.)

The Linux RTC framework has previously been a bit vague in this area, but
any other behavior is problematic and not very portable.  RTCs with full
YYYY-MM-DD HH:MM[:SS] alarms won't have a problem here.  Only ones with
partial match criteria, with the most visible example being the PC RTC, get
confused.  (Because the criteria will match repeatedly.)

Update comments relating to that oneshot behavior and timezone handling.
(Timezones are another issue that's mostly visible with rtc-cmos.  That's
because PCs often dual-boot MS-Windows, which likes its RTC to match local
wall-clock time instead of UTC.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index ab455ddb16cf..ff7539a4dbea 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -472,10 +472,22 @@ static struct cmos_rtc	cmos_rtc;
 static irqreturn_t cmos_interrupt(int irq, void *p)
 {
         u8              irqstat;
+        u8              rtc_control;
 
         spin_lock(&rtc_lock);
         irqstat = CMOS_READ(RTC_INTR_FLAGS);
-        irqstat &= (CMOS_READ(RTC_CONTROL) & RTC_IRQMASK) | RTC_IRQF;
+        rtc_control = CMOS_READ(RTC_CONTROL);
+        irqstat &= (rtc_control & RTC_IRQMASK) | RTC_IRQF;
+
+        /* All Linux RTC alarms should be treated as if they were oneshot.
+         * Similar code may be needed in system wakeup paths, in case the
+         * alarm woke the system.
+         */
+        if (irqstat & RTC_AIE) {
+                rtc_control &= ~RTC_AIE;
+                CMOS_WRITE(rtc_control, RTC_CONTROL);
+                CMOS_READ(RTC_INTR_FLAGS);
+        }
         spin_unlock(&rtc_lock);
 
         if (is_intr(irqstat)) {