rtc-at91rm9200: avoid spurious irqs

This fixes kernel http://bugzilla.kernel.org/show_bug.cgi?id=11112 (bogus
RTC update IRQs reported) for rtc-at91rm9200 by scrubbing old IRQ status
before enabling IRQs.

It also removes nonfunctional periodic IRQ support from this driver;
only update IRQs are reported, or provided by the hardware.

I suspect some other RTCs probably have versions of #11112; it's easy to
overlook, since most non-RTC drivers don't care about spurious IRQs:
they're not reported to userspace.

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, 6 insertions, 10 deletions

diff --git a/drivers/rtc/rtc-at91rm9200.c b/drivers/rtc/rtc-at91rm9200.c
index 9c3db934cc24..cd32d05db773 100644
--- a/drivers/rtc/rtc-at91rm9200.c
+++ b/drivers/rtc/rtc-at91rm9200.c
@@ -171,8 +171,10 @@ static int at91_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
                 | BIN2BCD(tm.tm_mday) << 24
                 | AT91_RTC_DATEEN | AT91_RTC_MTHEN);
 
-        if (alrm->enabled)
+        if (alrm->enabled) {
+                at91_sys_write(AT91_RTC_SCCR, AT91_RTC_ALARM);
                 at91_sys_write(AT91_RTC_IER, AT91_RTC_ALARM);
+        }
 
         pr_debug("%s(): %4d-%02d-%02d %02d:%02d:%02d\n", __func__,
                 at91_alarm_year, tm.tm_mon, tm.tm_mday, tm.tm_hour,
@@ -191,28 +193,22 @@ static int at91_rtc_ioctl(struct device *dev, unsigned int cmd,
 
         pr_debug("%s(): cmd=%08x, arg=%08lx.\n", __func__, cmd, arg);
 
+        /* important:  scrub old status before enabling IRQs */
         switch (cmd) {
         case RTC_AIE_OFF:       /* alarm off */
                 at91_sys_write(AT91_RTC_IDR, AT91_RTC_ALARM);
                 break;
         case RTC_AIE_ON:        /* alarm on */
+                at91_sys_write(AT91_RTC_SCCR, AT91_RTC_ALARM);
                 at91_sys_write(AT91_RTC_IER, AT91_RTC_ALARM);
                 break;
         case RTC_UIE_OFF:       /* update off */
-        case RTC_PIE_OFF:       /* periodic off */
                 at91_sys_write(AT91_RTC_IDR, AT91_RTC_SECEV);
                 break;
         case RTC_UIE_ON:        /* update on */
-        case RTC_PIE_ON:        /* periodic on */
+                at91_sys_write(AT91_RTC_SCCR, AT91_RTC_SECEV);
                 at91_sys_write(AT91_RTC_IER, AT91_RTC_SECEV);
                 break;
-        case RTC_IRQP_READ:     /* read periodic alarm frequency */
-                ret = put_user(AT91_RTC_FREQ, (unsigned long *) arg);
-                break;
-        case RTC_IRQP_SET:      /* set periodic alarm frequency */
-                if (arg != AT91_RTC_FREQ)
-                        ret = -EINVAL;
-                break;
         default:
                 ret = -ENOIOCTLCMD;
                 break;