[PATCH 4.14-openela 008/190] iio: addac: stx104: Fix race condition for stx104_write_raw()

[Sasha Levin <sashal@kernel.org>]

From: William Breathitt Gray <william.gray@linaro.org>

[ Upstream commit 9740827468cea80c42db29e7171a50e99acf7328 ]

The priv->chan_out_states array and actual DAC value can become
mismatched if stx104_write_raw() is called concurrently. Prevent such a
race condition by utilizing a mutex.

Fixes: 97a445dad37a ("iio: Add IIO support for the DAC on the Apex Embedded Systems STX104")
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/r/c95c9a77fcef36b2a052282146950f23bbc1ebdc.1680790580.git.william.gray@linaro.org
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iio/adc/stx104.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/iio/adc/stx104.c b/drivers/iio/adc/stx104.c
index 2da741d27540f..edc3b29eed621 100644
--- a/drivers/iio/adc/stx104.c
+++ b/drivers/iio/adc/stx104.c
@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
+#include <linux/mutex.h>
 #include <linux/spinlock.h>
 
 #define STX104_OUT_CHAN(chan) {				\
@@ -54,10 +55,12 @@ MODULE_PARM_DESC(base, "Apex Embedded Systems STX104 base addresses");
 
 /**
  * struct stx104_iio - IIO device private data structure
+ * @lock: synchronization lock to prevent I/O race conditions
  * @chan_out_states:	channels' output states
  * @base:		base port address of the IIO device
  */
 struct stx104_iio {
+	struct mutex lock;
 	unsigned int chan_out_states[STX104_NUM_OUT_CHAN];
 	unsigned int base;
 };
@@ -160,9 +163,12 @@ static int stx104_write_raw(struct iio_dev *indio_dev,
 			if ((unsigned int)val > 65535)
 				return -EINVAL;
 
+			mutex_lock(&priv->lock);
+
 			priv->chan_out_states[chan->channel] = val;
 			outw(val, priv->base + 4 + 2 * chan->channel);
 
+			mutex_unlock(&priv->lock);
 			return 0;
 		}
 		return -EINVAL;
@@ -323,6 +329,8 @@ static int stx104_probe(struct device *dev, unsigned int id)
 	priv = iio_priv(indio_dev);
 	priv->base = base[id];
 
+	mutex_init(&priv->lock);
+
 	/* configure device for software trigger operation */
 	outb(0, base[id] + 9);
 
-- 
2.43.0