[PATCH 4.19 024/129] iio: addac: stx104: Fix race condition when converting analog-to-digital

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: William Breathitt Gray <william.gray@xxxxxxxxxx>

[ Upstream commit 4f9b80aefb9e2f542a49d9ec087cf5919730e1dd ]

The ADC conversion procedure requires several device I/O operations
performed in a particular sequence. If stx104_read_raw() is called
concurrently, the ADC conversion procedure could be clobbered. Prevent
such a race condition by utilizing a mutex.

Fixes: 4075a283ae83 ("iio: stx104: Add IIO support for the ADC channels")
Signed-off-by: William Breathitt Gray <william.gray@xxxxxxxxxx>
Link: https://lore.kernel.org/r/2ae5e40eed5006ca735e4c12181a9ff5ced65547.1680790580.git.william.gray@xxxxxxxxxx
Cc: <Stable@xxxxxxxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/iio/adc/stx104.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iio/adc/stx104.c b/drivers/iio/adc/stx104.c
index 78e87d1aaaefb..49aeb76212fd0 100644
--- a/drivers/iio/adc/stx104.c
+++ b/drivers/iio/adc/stx104.c
@@ -125,6 +125,8 @@ static int stx104_read_raw(struct iio_dev *indio_dev,
 			return IIO_VAL_INT;
 		}
 
+		mutex_lock(&priv->lock);
+
 		/* select ADC channel */
 		iowrite8(chan->channel | (chan->channel << 4), &reg->achan);
 
@@ -135,6 +137,8 @@ static int stx104_read_raw(struct iio_dev *indio_dev,
 		while (ioread8(&reg->cir_asr) & BIT(7));
 
 		*val = ioread16(&reg->ssr_ad);
+
+		mutex_unlock(&priv->lock);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_OFFSET:
 		/* get ADC bipolar/unipolar configuration */
-- 
2.40.1