iio: dac: ad7303: replace mlock with own lock

This change replaces indio_dev's mlock with the driver's own lock. The lock
is mostly needed to protect state when changing the `dac_cache` info.
The lock has been extended to `ad7303_read_raw()`, to make sure that the
cache is updated if an SPI-write is already in progress.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/ad7303.c

@@ -41,6 +41,7 @@ struct ad7303_state {
 	struct regulator *vdd_reg;
 	struct regulator *vref_reg;
 
+	struct mutex lock;
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
 	 * transfer buffers to live in their own cache lines.
@@ -79,7 +80,7 @@ static ssize_t ad7303_write_dac_powerdown(struct iio_dev *indio_dev,
 	if (ret)
 		return ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 
 	if (pwr_down)
 		st->config |= AD7303_CFG_POWER_DOWN(chan->channel);
@@ -90,7 +91,7 @@ static ssize_t ad7303_write_dac_powerdown(struct iio_dev *indio_dev,
 	 * mode, so just write one of the DAC channels again */
 	ad7303_write(st, chan->channel, st->dac_cache[chan->channel]);
 
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 	return len;
 }
 
@@ -116,7 +117,9 @@ static int ad7303_read_raw(struct iio_dev *indio_dev,
 
 	switch (info) {
 	case IIO_CHAN_INFO_RAW:
+		mutex_lock(&st->lock);
 		*val = st->dac_cache[chan->channel];
+		mutex_unlock(&st->lock);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
 		vref_uv = ad7303_get_vref(st, chan);
@@ -144,11 +147,11 @@ static int ad7303_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 = ad7303_write(st, chan->address, val);
 		if (ret == 0)
 			st->dac_cache[chan->channel] = val;
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&st->lock);
 		break;
 	default:
 		ret = -EINVAL;
@@ -211,6 +214,8 @@ static int ad7303_probe(struct spi_device *spi)
 
 	st->spi = spi;
 
+	mutex_init(&st->lock);
+
 	st->vdd_reg = devm_regulator_get(&spi->dev, "Vdd");
 	if (IS_ERR(st->vdd_reg))
 		return PTR_ERR(st->vdd_reg);