rtc: ensure rtc_set_alarm fails when alarms are not supported

When using RTC_ALM_SET or RTC_WKALM_SET with rtc_wkalrm.enabled not set,
rtc_timer_enqueue() is not called and rtc_set_alarm() may succeed but the
subsequent RTC_AIE_ON ioctl will fail. RTC_ALM_READ would also fail in that
case.

Ensure rtc_set_alarm() fails when alarms are not supported to avoid letting
programs think the alarms are working for a particular RTC when they are
not.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 7cbdc9228dd5..6d4012dd6922 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -441,6 +441,11 @@ int rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
 {
         int err;
 
+        if (!rtc->ops)
+                return -ENODEV;
+        else if (!rtc->ops->set_alarm)
+                return -EINVAL;
+
         err = rtc_valid_tm(&alarm->time);
         if (err != 0)
                 return err;