staging: iio: ade7753: expanding buffer lock to cover both buffer and state protection

Dropping the extra lock (used for protecting the write frequency) by
expanding the buffer lock to cover both buffer and state protection.

Doing this by introducing a new function (__ade7753_spi_write_reg_16)
making buffer changes without locking the state, to avoid nested locks
while making device frequency changes.
Signed-off-by: Himanshi Jain <himshijain.hj@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/meter/ade7753.c

@@ -80,13 +80,11 @@
  * @us:         actual spi_device
  * @tx:         transmit buffer
  * @rx:         receive buffer
- * @buf_lock:       mutex to protect tx and rx
- * @lock:	protect sensor data
+ * @buf_lock:       mutex to protect tx, rx and write frequency
  **/
 struct ade7753_state {
 	struct spi_device   *us;
 	struct mutex        buf_lock;
-	struct mutex	    lock; /* protect sensor data */
 	u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
 	u8          rx[ADE7753_MAX_RX];
 };
@@ -109,18 +107,28 @@ static int ade7753_spi_write_reg_8(struct device *dev,
 	return ret;
 }
 
-static int ade7753_spi_write_reg_16(struct device *dev, u8 reg_address,
+static int __ade7753_spi_write_reg_16(struct device *dev, u8 reg_address,
 				      u16 value)
 {
-	int ret;
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct ade7753_state *st = iio_priv(indio_dev);
 
-	mutex_lock(&st->buf_lock);
 	st->tx[0] = ADE7753_WRITE_REG(reg_address);
 	st->tx[1] = (value >> 8) & 0xFF;
 	st->tx[2] = value & 0xFF;
-	ret = spi_write(st->us, st->tx, 3);
+
+	return spi_write(st->us, st->tx, 3);
+}
+
+static int ade7753_spi_write_reg_16(struct device *dev, u8 reg_address,
+				    u16 value)
+{
+	int ret;
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct ade7753_state *st = iio_priv(indio_dev);
+
+	mutex_lock(&st->buf_lock);
+	ret = __ade7753_spi_write_reg_16(dev, reg_address, value);
 	mutex_unlock(&st->buf_lock);
 
 	return ret;
@@ -485,7 +493,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
 	if (!val)
 		return -EINVAL;
 
-	mutex_lock(&st->lock);
+	mutex_lock(&st->buf_lock);
 
 	t = 27900 / val;
 	if (t > 0)
@@ -503,10 +511,10 @@ static ssize_t ade7753_write_frequency(struct device *dev,
 	reg &= ~(3 << 11);
 	reg |= t << 11;
 
-	ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
+	ret = __ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
 
 out:
-	mutex_unlock(&st->lock);
+	mutex_unlock(&st->buf_lock);
 
 	return ret ? ret : len;
 }
@@ -581,7 +589,6 @@ static int ade7753_probe(struct spi_device *spi)
 	st = iio_priv(indio_dev);
 	st->us = spi;
 	mutex_init(&st->buf_lock);
-	mutex_init(&st->lock);
 
 	indio_dev->name = spi->dev.driver->name;
 	indio_dev->dev.parent = &spi->dev;