iio: addac: stx104: Fix race condition when converting analog-to-digital

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@linaro.org>
Link: https://lore.kernel.org/r/2ae5e40eed5006ca735e4c12181a9ff5ced65547.1680790580.git.william.gray@linaro.org
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/addac/stx104.c b/drivers/iio/addac/stx104.c
index 4239aafe42fc8c8ee27c278c6b2cfc5279fc2c97..8730b79e921c83717e0c3b8e10d860f4be604e98 100644 (file)
--- a/drivers/iio/addac/stx104.c
+++ b/drivers/iio/addac/stx104.c
@@ -117,6 +117,8 @@ 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);
 
@@ -127,6 +129,8 @@ 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 */