staging: iio: ad9834: Use private driver lock instead of mlock

iio_dev->mlock should be used by the IIO core only for protecting
device operating mode changes. ie. Changes between INDIO_DIRECT_MODE,
INDIO_BUFFER_* modes.
Replace mlock with a lock in the device's global data to protect
hardware state changes.

Signed-off-by: sayli karnik <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/staging/iio/frequency/ad9834.c

···
  * @msg:		default spi message
  * @freq_xfer:		tuning word spi transfer
  * @freq_msg:		tuning word spi message
+ * @lock:		protect sensor state
  * @data:		spi transmit buffer
  * @freq_data:		tuning word spi transmit buffer
  */
···
 	struct spi_message		msg;
 	struct spi_transfer		freq_xfer[2];
 	struct spi_message		freq_msg;
+	struct mutex                    lock;   /* protect sensor state */
 
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
···
 	if (ret)
 		goto error_ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 	switch ((u32)this_attr->address) {
 	case AD9834_REG_FREQ0:
 	case AD9834_REG_FREQ1:
···
 	default:
 		ret = -ENODEV;
 	}
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 
 error_ret:
 	return ret ? ret : len;
···
 	int ret = 0;
 	bool is_ad9833_7 = (st->devid == ID_AD9833) || (st->devid == ID_AD9837);
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 
 	switch ((u32)this_attr->address) {
 	case 0:
···
 		st->data = cpu_to_be16(AD9834_REG_CMD | st->control);
 		ret = spi_sync(st->spi, &st->msg);
 	}
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 
 	return ret ? ret : len;
 }
···
 	}
 	spi_set_drvdata(spi, indio_dev);
 	st = iio_priv(indio_dev);
+	mutex_init(&st->lock);
 	st->mclk = pdata->mclk;
 	st->spi = spi;
 	st->devid = spi_get_device_id(spi)->driver_data;