iio: common: st_sensors: fix possible infinite loop in st_sensors_irq_thread

Return a boolean value in st_sensors_new_samples_available routine in
order to avoid an infinite loop in st_sensors_irq_thread if
stat_drdy.addr is not defined or stat_drdy read fails

Fixes: 90efe055 ("iio: st_sensors: harden interrupt handling")
Reported-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/c9ec69ed349e7200c779fd7a5bf04c1aaa2817aa.1607438132.git.lorenzo@kernel.org
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/common/st_sensors/st_sensors_trigger.c

@@ -23,35 +23,31 @@
  * @sdata: Sensor data.
  *
  * returns:
- * 0 - no new samples available
- * 1 - new samples available
- * negative - error or unknown
+ * false - no new samples available or read error
+ * true - new samples available
  */
-static int st_sensors_new_samples_available(struct iio_dev *indio_dev,
+static bool st_sensors_new_samples_available(struct iio_dev *indio_dev,
 					     struct st_sensor_data *sdata)
 {
 	int ret, status;
 
 	/* How would I know if I can't check it? */
 	if (!sdata->sensor_settings->drdy_irq.stat_drdy.addr)
-		return -EINVAL;
+		return true;
 
 	/* No scan mask, no interrupt */
 	if (!indio_dev->active_scan_mask)
-		return 0;
+		return false;
 
 	ret = regmap_read(sdata->regmap,
 			  sdata->sensor_settings->drdy_irq.stat_drdy.addr,
 			  &status);
 	if (ret < 0) {
 		dev_err(sdata->dev, "error checking samples available\n");
-		return ret;
+		return false;
 	}
 
-	if (status & sdata->sensor_settings->drdy_irq.stat_drdy.mask)
-		return 1;
-
-	return 0;
+	return !!(status & sdata->sensor_settings->drdy_irq.stat_drdy.mask);
 }
 
 /**
@@ -180,9 +176,15 @@ int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
 
 	/* Tell the interrupt handler that we're dealing with edges */
 	if (irq_trig == IRQF_TRIGGER_FALLING ||
-	    irq_trig == IRQF_TRIGGER_RISING)
+	    irq_trig == IRQF_TRIGGER_RISING) {
+		if (!sdata->sensor_settings->drdy_irq.stat_drdy.addr) {
+			dev_err(&indio_dev->dev,
+				"edge IRQ not supported w/o stat register.\n");
+			err = -EOPNOTSUPP;
+			goto iio_trigger_free;
+		}
 		sdata->edge_irq = true;
-	else
+	} else {
 		/*
 		 * If we're not using edges (i.e. level interrupts) we
 		 * just mask off the IRQ, handle one interrupt, then
@@ -190,6 +192,7 @@ int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
 		 * interrupt handler top half again and start over.
 		 */
 		irq_trig |= IRQF_ONESHOT;
+	}
 
 	/*
 	 * If the interrupt pin is Open Drain, by definition this