staging: ad7606: Replace mlock with driver private lock

The IIO subsystem is redefining iio_dev->mlock to be used by
the IIO core only for protecting device operating mode changes.
ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.

In this driver, mlock was being used to protect hardware state
changes. Replace it with a lock in the devices global data.

Signed-off-by: Arushi Singhal <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/staging/iio/adc/ad7606.c

···
 	switch (mask) {
 	case IIO_CHAN_INFO_SCALE:
 		ret = -EINVAL;
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&st->lock);
 		for (i = 0; i < ARRAY_SIZE(scale_avail); i++)
 			if (val2 == scale_avail[i][1]) {
 				gpiod_set_value(st->gpio_range, i);
···
 				ret = 0;
 				break;
 			}
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&st->lock);
 
 		return ret;
 	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
···
 		values[1] = (ret >> 1) & 1;
 		values[2] = (ret >> 2) & 1;
 
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&st->lock);
 		gpiod_set_array_value(ARRAY_SIZE(values), st->gpio_os->desc,
 				      values);
 		st->oversampling = val;
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&st->lock);
 
 		return 0;
 	default:
···
 	st = iio_priv(indio_dev);
 
 	st->dev = dev;
+	mutex_init(&st->lock);
 	st->bops = bops;
 	st->base_address = base_address;
 	/* tied to logic low, analog input range is +/- 5V */

drivers/staging/iio/adc/ad7606.h

···
  * @name:		identification string for chip
  * @channels:		channel specification
  * @num_channels:	number of channels
+ * @lock		protect sensor state
  */
 
 struct ad7606_chip_info {
···
 
 /**
  * struct ad7606_state - driver instance specific data
+ * @lock		protect sensor state
  */
 
 struct ad7606_state {
···
 	bool				done;
 	void __iomem			*base_address;
 
+	struct mutex			lock; /* protect sensor state */
 	struct gpio_desc		*gpio_convst;
 	struct gpio_desc		*gpio_reset;
 	struct gpio_desc		*gpio_range;