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From:   William Breathitt Gray <william.gray@linaro.org>
To:     Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>
Cc:     linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        William Breathitt Gray <william.gray@linaro.org>
Subject: [PATCH v4 2/5] iio: addac: stx104: Fix race condition when converting analog-to-digital
Date:   Tue,  4 Apr 2023 10:11:59 -0400
Message-Id: <2ae5e40eed5006ca735e4c12181a9ff5ced65547.1680564468.git.william.gray@linaro.org>
In-Reply-To: <cover.1680564468.git.william.gray@linaro.org>
References: <cover.1680564468.git.william.gray@linaro.org>
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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>
---
 drivers/iio/addac/stx104.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iio/addac/stx104.c b/drivers/iio/addac/stx104.c
index 4239aafe42fc..8730b79e921c 100644
--- 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 */
-- 
2.39.2