iio: chemical: bme680: Fix read/write ops to device by adding mutexes

[ Upstream commit 77641e5 ]

Add mutexes in the {read/write}_raw() functions of the device to guard the
read/write of data from/to the device. This is necessary because for any
operation other than temperature, multiple reads need to take place from
the device. Even though regmap has a locking by itself, it won't protect us
from multiple applications trying to read at the same time temperature and
pressure since the pressure reading includes an internal temperature
reading and there is nothing to ensure that this temperature+pressure
reading will happen sequentially without any other operation interfering
in the meantime.

Fixes: 1b3bd85 ("iio: chemical: Add support for Bosch BME680 sensor")
Signed-off-by: Vasileios Amoiridis <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jonathan Cameron <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: vamoirid

drivers/iio/chemical/bme680_core.c

@@ -10,6 +10,7 @@
  */
 #include <linux/acpi.h>
 #include <linux/bitfield.h>
+#include <linux/cleanup.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/module.h>
@@ -52,6 +53,7 @@ struct bme680_calib {
 struct bme680_data {
 	struct regmap *regmap;
 	struct bme680_calib bme680;
+	struct mutex lock; /* Protect multiple serial R/W ops to device. */
 	u8 oversampling_temp;
 	u8 oversampling_press;
 	u8 oversampling_humid;
@@ -827,6 +829,8 @@ static int bme680_read_raw(struct iio_dev *indio_dev,
 {
 	struct bme680_data *data = iio_priv(indio_dev);
 
+	guard(mutex)(&data->lock);
+
 	switch (mask) {
 	case IIO_CHAN_INFO_PROCESSED:
 		switch (chan->type) {
@@ -871,6 +875,8 @@ static int bme680_write_raw(struct iio_dev *indio_dev,
 {
 	struct bme680_data *data = iio_priv(indio_dev);
 
+	guard(mutex)(&data->lock);
+
 	if (val2 != 0)
 		return -EINVAL;
 
@@ -967,6 +973,7 @@ int bme680_core_probe(struct device *dev, struct regmap *regmap,
 		name = bme680_match_acpi_device(dev);
 
 	data = iio_priv(indio_dev);
+	mutex_init(&data->lock);
 	dev_set_drvdata(dev, indio_dev);
 	data->regmap = regmap;
 	indio_dev->name = name;