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

commit 4f9b80aefb9e2f542a49d9ec087cf5919730e1dd upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/iio/addac/stx104.c b/drivers/iio/addac/stx104.c
index 48a91a95e597b306a3bd194d7f26d90c10b6fc58..46b46b7a3c8ded0080acc8a12002f619d0d4553e 100644 (file)
--- a/drivers/iio/addac/stx104.c
+++ b/drivers/iio/addac/stx104.c
@@ -114,6 +114,8 @@ 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);
 
@@ -124,6 +126,8 @@ 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 */