rtc: expose RTC_FEATURE_UPDATE_INTERRUPT

Set RTC_FEATURE_UPDATE_INTERRUPT by default and clear it when it is not
supported.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211018152337.78732-1-alexandre.belloni@bootlin.com

drivers/rtc/class.c

@@ -232,6 +232,7 @@ static struct rtc_device *rtc_allocate_device(void)
 	rtc->pie_enabled = 0;
 
 	set_bit(RTC_FEATURE_ALARM, rtc->features);
+	set_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
 
 	return rtc;
 }
@@ -389,6 +390,9 @@ int __devm_rtc_register_device(struct module *owner, struct rtc_device *rtc)
 	if (!rtc->ops->set_alarm)
 		clear_bit(RTC_FEATURE_ALARM, rtc->features);
 
+	if (rtc->uie_unsupported)
+		clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
+
 	if (rtc->ops->set_offset)
 		set_bit(RTC_FEATURE_CORRECTION, rtc->features);
 

drivers/rtc/interface.c

@@ -561,7 +561,8 @@ int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
 	if (rtc->uie_rtctimer.enabled == enabled)
 		goto out;
 
-	if (rtc->uie_unsupported || !test_bit(RTC_FEATURE_ALARM, rtc->features)) {
+	if (!test_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features) ||
+	    !test_bit(RTC_FEATURE_ALARM, rtc->features)) {
 		mutex_unlock(&rtc->ops_lock);
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
 		return rtc_dev_update_irq_enable_emul(rtc, enabled);