[PATCH v6 03/12] iio: dac: ad5686: acquire lock when doing powerdown control

[Rodrigo Alencar via B4 Relay <devnull+rodrigo.alencar.analog.com@kernel.org>]

From: Rodrigo Alencar <rodrigo.alencar@analog.com>

Protect access of pwr_down_mode and pwr_down_mask fields with existing
mutex lock. Each channel exposes their own attributes for controlling
powerdown modes and powerdown state. This fixes potential race conditions
as those the write functions perform non-atomic read-modify-write
operations to those pwr_down_* fields. This issue exists since the ad5686
driver was first introduced.

Fixes: c2f37c8dcadc ("iio: dac: New driver for AD5686R, AD5685R, AD5684R Digital to analog converters")
Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
---
 drivers/iio/dac/ad5686.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/iio/dac/ad5686.c b/drivers/iio/dac/ad5686.c
index 076fe8b8bd85..9eb6b61c471d 100644
--- a/drivers/iio/dac/ad5686.c
+++ b/drivers/iio/dac/ad5686.c
@@ -30,6 +30,8 @@ static int ad5686_get_powerdown_mode(struct iio_dev *indio_dev,
 {
 	struct ad5686_state *st = iio_priv(indio_dev);
 
+	guard(mutex)(&st->lock);
+
 	return ((st->pwr_down_mode >> (chan->channel * 2)) & 0x3) - 1;
 }
 
@@ -39,6 +41,8 @@ static int ad5686_set_powerdown_mode(struct iio_dev *indio_dev,
 {
 	struct ad5686_state *st = iio_priv(indio_dev);
 
+	guard(mutex)(&st->lock);
+
 	st->pwr_down_mode &= ~(0x3 << (chan->channel * 2));
 	st->pwr_down_mode |= ((mode + 1) << (chan->channel * 2));
 
@@ -57,6 +61,8 @@ static ssize_t ad5686_read_dac_powerdown(struct iio_dev *indio_dev,
 {
 	struct ad5686_state *st = iio_priv(indio_dev);
 
+	guard(mutex)(&st->lock);
+
 	return sysfs_emit(buf, "%d\n", !!(st->pwr_down_mask &
 				       (0x3 << (chan->channel * 2))));
 }
@@ -77,6 +83,8 @@ static ssize_t ad5686_write_dac_powerdown(struct iio_dev *indio_dev,
 	if (ret)
 		return ret;
 
+	guard(mutex)(&st->lock);
+
 	if (readin)
 		st->pwr_down_mask |= (0x3 << (chan->channel * 2));
 	else

-- 
2.43.0