iio: dac: ti-dac7612: 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 on the device's state from potential concurrent write
accesses from userspace. The write operation requires an SPI write, then
toggling of a GPIO, so the lock aims to protect the sanity of the entire
sequence of operation.

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/20200916092535.76527-1-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/dac/ti-dac7612.c b/drivers/iio/dac/ti-dac7612.c
index 07c9f39..4c0f4b5 100644 (file)
--- a/drivers/iio/dac/ti-dac7612.c
+++ b/drivers/iio/dac/ti-dac7612.c
@@ -23,6 +23,14 @@ struct dac7612 {
        uint16_t cache[2];
 
        /*
+        * Lock to protect the state of the device from potential concurrent
+        * write accesses from userspace. The write operation requires an
+        * SPI write, then toggling of a GPIO, so the lock aims to protect
+        * the sanity of the entire sequence of operation.
+        */
+       struct mutex lock;
+
+       /*
         * DMA (thus cache coherency maintenance) requires the
         * transfer buffers to live in their own cache lines.
         */
@@ -101,9 +109,9 @@ static int dac7612_write_raw(struct iio_dev *iio_dev,
        if (val == priv->cache[chan->channel])
                return 0;
 
-       mutex_lock(&iio_dev->mlock);
+       mutex_lock(&priv->lock);
        ret = dac7612_cmd_single(priv, chan->channel, val);
-       mutex_unlock(&iio_dev->mlock);
+       mutex_unlock(&priv->lock);
 
        return ret;
 }
@@ -145,6 +153,8 @@ static int dac7612_probe(struct spi_device *spi)
        iio_dev->num_channels = ARRAY_SIZE(priv->cache);
        iio_dev->name = spi_get_device_id(spi)->name;
 
+       mutex_init(&priv->lock);
+
        for (i = 0; i < ARRAY_SIZE(priv->cache); i++) {
                ret = dac7612_cmd_single(priv, i, 0);
                if (ret)