alarmtimer: Check RTC features instead of ops

RTC drivers used to leave .set_alarm() NULL in order to signal the RTC
device doesn't support alarms. The drivers are now clearing the
RTC_FEATURE_ALARM bit for that purpose in order to keep the rtc_class_ops
structure const. So now, .set_alarm() is set unconditionally and this
possibly causes the alarmtimer code to select an RTC device that doesn't
support alarms.

Test RTC_FEATURE_ALARM instead of relying on ops->set_alarm to determine
whether alarms are available.

Fixes: 634bd947f750 ("rtc: introduce features bitfield")
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210511014516.563031-1-alexandre.belloni@bootlin.com

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index bea9d08b16988b33a82b7d911c3a174bd4a0bb16..5897828b9d7ed98c3a06a465027a350006d47933 100644 (file)
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -92,7 +92,7 @@ static int alarmtimer_rtc_add_device(struct device *dev,
        if (rtcdev)
                return -EBUSY;
 
-       if (!rtc->ops->set_alarm)
+       if (!test_bit(RTC_FEATURE_ALARM, rtc->features))
                return -1;
        if (!device_may_wakeup(rtc->dev.parent))
                return -1;