rtc: Provide flag for rtc devices that don't support UIE

Richard Weinberger noticed that on some RTC hardware that
doesn't support UIE mode, due to coarse granular alarms
(like 1minute resolution), the current virtualized RTC
support doesn't properly error out when UIE is enabled.

Instead the current code queues an alarm for the next second,
but it won't fire until up to a miniute later.

This patch provides a generic way to flag this sort of hardware
and fixes the issue on the mpc5121 where Richard noticed the
problem.

CC: stable@vger.kernel.org
Reported-by: Richard Weinberger <richard@nod.at>
Tested-by: Richard Weinberger <richard@nod.at>
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 93f4d035076b..fcabfb4873c8 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -202,7 +202,8 @@ struct rtc_device
         struct hrtimer pie_timer; /* sub second exp, so needs hrtimer */
         int pie_enabled;
         struct work_struct irqwork;
-
+        /* Some hardware can't support UIE mode */
+        int uie_unsupported;
 
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
         struct work_struct uie_task;