iio:dac:ad5064 mlock cleanup - move to a local lock.

indio_dev->mlock is intended to protect state transitions in
the core. It's scope is tightly defined. For device specific
uses such as those made here, we should define a local lock
allowing the scope of the lock to be defined near to what it
is protecting.

These mlock changes can be non obvious, but given we don't do
anything other than direct for DACs, these ones are easy to do.

If anyone wants to help with this particular effort it would
be most welcome!
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/ad5064.c

@@ -112,6 +112,8 @@ struct ad5064_state {
 	bool				use_internal_vref;
 
 	ad5064_write_func		write;
+	/* Lock used to maintain consistency between cached and dev state */
+	struct mutex lock;
 
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
@@ -248,11 +250,11 @@ static int ad5064_set_powerdown_mode(struct iio_dev *indio_dev,
 	struct ad5064_state *st = iio_priv(indio_dev);
 	int ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 	st->pwr_down_mode[chan->channel] = mode + 1;
 
 	ret = ad5064_sync_powerdown_mode(st, chan);
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 
 	return ret;
 }
@@ -291,11 +293,11 @@ static ssize_t ad5064_write_dac_powerdown(struct iio_dev *indio_dev,
 	if (ret)
 		return ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 	st->pwr_down[chan->channel] = pwr_down;
 
 	ret = ad5064_sync_powerdown_mode(st, chan);
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 	return ret ? ret : len;
 }
 
@@ -349,12 +351,12 @@ static int ad5064_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 = ad5064_write(st, AD5064_CMD_WRITE_INPUT_N_UPDATE_N,
 				chan->address, val, chan->scan_type.shift);
 		if (ret == 0)
 			st->dac_cache[chan->channel] = val;
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&st->lock);
 		break;
 	default:
 		ret = -EINVAL;
@@ -856,6 +858,7 @@ static int ad5064_probe(struct device *dev, enum ad5064_type type,
 		return  -ENOMEM;
 
 	st = iio_priv(indio_dev);
+	mutex_init(&st->lock);
 	dev_set_drvdata(dev, indio_dev);
 
 	st->chip_info = &ad5064_chip_info_tbl[type];