iio: st_sensors: Add a local lock for protecting odr

Right now the (framework) mlock lock is (ab)used for multiple purposes:
1- protecting concurrent accesses over the odr local cache
2- avoid changing samplig frequency whilst buffer is running

Let's start by handling situation #1 with a local lock.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Cc: Denis Ciocca <denis.ciocca@st.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20220207143840.707510-7-miquel.raynal@bootlin.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/common/st_sensors/st_sensors_core.c

@@ -71,16 +71,18 @@ st_sensors_match_odr_error:
 
 int st_sensors_set_odr(struct iio_dev *indio_dev, unsigned int odr)
 {
-	int err;
+	int err = 0;
 	struct st_sensor_odr_avl odr_out = {0, 0};
 	struct st_sensor_data *sdata = iio_priv(indio_dev);
 
+	mutex_lock(&sdata->odr_lock);
+
 	if (!sdata->sensor_settings->odr.mask)
-		return 0;
+		goto unlock_mutex;
 
 	err = st_sensors_match_odr(sdata->sensor_settings, odr, &odr_out);
 	if (err < 0)
-		goto st_sensors_match_odr_error;
+		goto unlock_mutex;
 
 	if ((sdata->sensor_settings->odr.addr ==
 					sdata->sensor_settings->pw.addr) &&
@@ -103,7 +105,9 @@ int st_sensors_set_odr(struct iio_dev *indio_dev, unsigned int odr)
 	if (err >= 0)
 		sdata->odr = odr_out.hz;
 
-st_sensors_match_odr_error:
+unlock_mutex:
+	mutex_unlock(&sdata->odr_lock);
+
 	return err;
 }
 EXPORT_SYMBOL_NS(st_sensors_set_odr, IIO_ST_SENSORS);
@@ -361,6 +365,8 @@ int st_sensors_init_sensor(struct iio_dev *indio_dev,
 	struct st_sensors_platform_data *of_pdata;
 	int err = 0;
 
+	mutex_init(&sdata->odr_lock);
+
 	/* If OF/DT pdata exists, it will take precedence of anything else */
 	of_pdata = st_sensors_dev_probe(indio_dev->dev.parent, pdata);
 	if (IS_ERR(of_pdata))
@@ -554,18 +560,24 @@ int st_sensors_read_info_raw(struct iio_dev *indio_dev,
 		err = -EBUSY;
 		goto out;
 	} else {
+		mutex_lock(&sdata->odr_lock);
 		err = st_sensors_set_enable(indio_dev, true);
-		if (err < 0)
+		if (err < 0) {
+			mutex_unlock(&sdata->odr_lock);
 			goto out;
+		}
 
 		msleep((sdata->sensor_settings->bootime * 1000) / sdata->odr);
 		err = st_sensors_read_axis_data(indio_dev, ch, val);
-		if (err < 0)
+		if (err < 0) {
+			mutex_unlock(&sdata->odr_lock);
 			goto out;
+		}
 
 		*val = *val >> ch->scan_type.shift;
 
 		err = st_sensors_set_enable(indio_dev, false);
+		mutex_unlock(&sdata->odr_lock);
 	}
 out:
 	mutex_unlock(&indio_dev->mlock);

include/linux/iio/common/st_sensors.h

@@ -237,6 +237,7 @@ struct st_sensor_settings {
  * @hw_irq_trigger: if we're using the hardware interrupt on the sensor.
  * @hw_timestamp: Latest timestamp from the interrupt handler, when in use.
  * @buffer_data: Data used by buffer part.
+ * @odr_lock: Local lock for preventing concurrent ODR accesses/changes
  */
 struct st_sensor_data {
 	struct iio_trigger *trig;
@@ -261,6 +262,8 @@ struct st_sensor_data {
 	s64 hw_timestamp;
 
 	char buffer_data[ST_SENSORS_MAX_BUFFER_SIZE] ____cacheline_aligned;
+
+	struct mutex odr_lock;
 };
 
 #ifdef CONFIG_IIO_BUFFER