iio: adc: fsl-imx25-gcq: Replace indio_dev->mlock with own device lock

As part of the general cleanup of indio_dev->mlock, this change replaces
it with a local lock, to protect against any other accesses during the
reading of sample. Reading a sample requires multiple consecutive regmap
operations and a completion callback, so this requires that no other
read occurs until it completes.

This is part of a bigger cleanup.
Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/
Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20200916092928.78026-1-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/fsl-imx25-gcq.c b/drivers/iio/adc/fsl-imx25-gcq.c
index 8cb51cf7a81645cd29052f9b9b49c693c408cf77..ab5139e911c32ebded0dee68e06807541446cc67 100644 (file)
--- a/drivers/iio/adc/fsl-imx25-gcq.c
+++ b/drivers/iio/adc/fsl-imx25-gcq.c
@@ -40,6 +40,15 @@ struct mx25_gcq_priv {
        int irq;
        struct regulator *vref[4];
        u32 channel_vref_mv[MX25_NUM_CFGS];
+       /*
+        * Lock to protect the device state during a potential concurrent
+        * read access from userspace. Reading a raw value requires a sequence
+        * of register writes, then a wait for a completion callback,
+        * and finally a register read, during which userspace could issue
+        * another read request. This lock protects a read access from
+        * ocurring before another one has finished.
+        */
+       struct mutex lock;
 };
 
 #define MX25_CQG_CHAN(chan, id) {\
@@ -137,9 +146,9 @@ static int mx25_gcq_read_raw(struct iio_dev *indio_dev,
 
        switch (mask) {
        case IIO_CHAN_INFO_RAW:
-               mutex_lock(&indio_dev->mlock);
+               mutex_lock(&priv->lock);
                ret = mx25_gcq_get_raw_value(&indio_dev->dev, chan, priv, val);
-               mutex_unlock(&indio_dev->mlock);
+               mutex_unlock(&priv->lock);
                return ret;
 
        case IIO_CHAN_INFO_SCALE:
@@ -314,6 +323,8 @@ static int mx25_gcq_probe(struct platform_device *pdev)
                return PTR_ERR(priv->regs);
        }
 
+       mutex_init(&priv->lock);
+
        init_completion(&priv->completed);
 
        ret = mx25_gcq_setup_cfgs(pdev, priv);