staging:iio-trig-periodic-rtc: Allow to reset frequency to 0

periodic rtc trigger initially has frequency 0

it is possible to change trigger frequency on-the-fly, but it is not
possible to set frequency back to 0

this patch allows to set trigger frequency to 0, thereby disabling
the rtc interrupt
Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/trigger/iio-trig-periodic-rtc.c

@@ -26,16 +26,22 @@ struct iio_prtc_trigger_info {
 	struct rtc_device *rtc;
 	int frequency;
 	struct rtc_task task;
+	bool state;
 };
 
 static int iio_trig_periodic_rtc_set_state(struct iio_trigger *trig, bool state)
 {
 	struct iio_prtc_trigger_info *trig_info = iio_trigger_get_drvdata(trig);
-	if (trig_info->frequency == 0)
+	int ret;
+	if (trig_info->frequency == 0 && state)
 		return -EINVAL;
 	dev_dbg(&trig_info->rtc->dev, "trigger frequency is %d\n",
 			trig_info->frequency);
-	return rtc_irq_set_state(trig_info->rtc, &trig_info->task, state);
+	ret = rtc_irq_set_state(trig_info->rtc, &trig_info->task, state);
+	if (ret == 0)
+		trig_info->state = state;
+
+	return ret;
 }
 
 static ssize_t iio_trig_periodic_read_freq(struct device *dev,
@@ -61,7 +67,14 @@ static ssize_t iio_trig_periodic_write_freq(struct device *dev,
 	if (ret)
 		goto error_ret;
 
-	ret = rtc_irq_set_freq(trig_info->rtc, &trig_info->task, val);
+	if (val > 0) {
+		ret = rtc_irq_set_freq(trig_info->rtc, &trig_info->task, val);
+		if (ret == 0 && trig_info->state && trig_info->frequency == 0)
+			ret = rtc_irq_set_state(trig_info->rtc, &trig_info->task, 1);
+	} else if (val == 0) {
+		ret = rtc_irq_set_state(trig_info->rtc, &trig_info->task, 0);
+	} else
+		ret = -EINVAL;
 	if (ret)
 		goto error_ret;