rtc: s5m: signal the core when alarm are not available

Clear the RTC_FEATURE_ALARM bit to signal to the core when alarms are not
available to ensure the alarm callbacks are never called and userspace is
aware alarms are not supported.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210804104133.5158-2-alexandre.belloni@bootlin.com

drivers/rtc/rtc-s5m.c

@@ -794,25 +794,20 @@ static int s5m_rtc_probe(struct platform_device *pdev)
 
 	info->rtc_dev->ops = &s5m_rtc_ops;
 
-	err = devm_rtc_register_device(info->rtc_dev);
-	if (err)
-		return err;
-
 	if (!info->irq) {
-		dev_info(&pdev->dev, "Alarm IRQ not available\n");
-		return 0;
-	}
-
-	ret = devm_request_threaded_irq(&pdev->dev, info->irq, NULL,
-					s5m_rtc_alarm_irq, 0, "rtc-alarm0",
-					info);
-	if (ret < 0) {
-		dev_err(&pdev->dev, "Failed to request alarm IRQ: %d: %d\n",
-			info->irq, ret);
-		return ret;
+		clear_bit(RTC_FEATURE_ALARM, info->rtc_dev->features);
+	} else {
+		ret = devm_request_threaded_irq(&pdev->dev, info->irq, NULL,
+						s5m_rtc_alarm_irq, 0, "rtc-alarm0",
+						info);
+		if (ret < 0) {
+			dev_err(&pdev->dev, "Failed to request alarm IRQ: %d: %d\n",
+				info->irq, ret);
+			return ret;
+		}
 	}
 
-	return 0;
+	return devm_rtc_register_device(info->rtc_dev);
 }
 
 #ifdef CONFIG_PM_SLEEP