[PATCH v4 03/13] 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 write 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 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")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
---
 drivers/iio/dac/ad5686.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iio/dac/ad5686.c b/drivers/iio/dac/ad5686.c
index 076fe8b8bd85..69358dd66cbc 100644
--- a/drivers/iio/dac/ad5686.c
+++ b/drivers/iio/dac/ad5686.c
@@ -39,6 +39,8 @@ 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));
 
@@ -77,6 +79,8 @@ 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