iio: dac: ad5686: 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 structure.
Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/ad5686.c

@@ -127,9 +127,9 @@ static int ad5686_read_raw(struct iio_dev *indio_dev,
 
 	switch (m) {
 	case IIO_CHAN_INFO_RAW:
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&st->lock);
 		ret = st->read(st, chan->address);
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&st->lock);
 		if (ret < 0)
 			return ret;
 		*val = (ret >> chan->scan_type.shift) &
@@ -157,12 +157,12 @@ static int ad5686_write_raw(struct iio_dev *indio_dev,
 		if (val > (1 << chan->scan_type.realbits) || val < 0)
 			return -EINVAL;
 
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&st->lock);
 		ret = st->write(st,
 				AD5686_CMD_WRITE_INPUT_N_UPDATE_N,
 				chan->address,
 				val << chan->scan_type.shift);
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&st->lock);
 		break;
 	default:
 		ret = -EINVAL;
@@ -468,6 +468,8 @@ int ad5686_probe(struct device *dev,
 	indio_dev->channels = st->chip_info->channels;
 	indio_dev->num_channels = st->chip_info->num_channels;
 
+	mutex_init(&st->lock);
+
 	switch (st->chip_info->regmap_type) {
 	case AD5310_REGMAP:
 		cmd = AD5686_CMD_CONTROL_REG;

drivers/iio/dac/ad5686.h

@@ -117,6 +117,7 @@ struct ad5686_chip_info {
  * @pwr_down_mask:	power down mask
  * @pwr_down_mode:	current power down mode
  * @use_internal_vref:	set to true if the internal reference voltage is used
+ * @lock		lock to protect the data buffer during regmap ops
  * @data:		spi transfer buffers
  */
 
@@ -130,6 +131,7 @@ struct ad5686_state {
 	ad5686_write_func		write;
 	ad5686_read_func		read;
 	bool				use_internal_vref;
+	struct mutex			lock;
 
 	/*
 	 * DMA (thus cache coherency maintenance) requires the