iio: accel: bmc150: optimize transfers in trigger handler

Some i2c busses (e.g.: Synopsys DesignWare I2C adapter) need to
enable/disable the bus at each i2c transfer and must wait for
the enable/disable to happen before sending the data.

When reading data in the trigger handler, the bmc150 accel driver does
one bus transfer for each axis. This has an impact on the frequency
of the accelerometer at high sample rates due to additional delays
introduced by the bus at each transfer.

Reading all axis values in one bus transfer reduces the delays
introduced by the bus.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/accel/bmc150-accel-core.c

@@ -989,6 +989,7 @@ static const struct iio_event_spec bmc150_accel_event = {
 		.realbits = (bits),					\
 		.storagebits = 16,					\
 		.shift = 16 - (bits),					\
+		.endianness = IIO_LE,					\
 	},								\
 	.event_spec = &bmc150_accel_event,				\
 	.num_event_specs = 1						\
@@ -1114,21 +1115,14 @@ static irqreturn_t bmc150_accel_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct bmc150_accel_data *data = iio_priv(indio_dev);
-	int bit, ret, i = 0;
-	unsigned int raw_val;
+	int ret;
 
 	mutex_lock(&data->mutex);
-	for (bit = 0; bit < AXIS_MAX; bit++) {
-		ret = regmap_bulk_read(data->regmap,
-				       BMC150_ACCEL_AXIS_TO_REG(bit), &raw_val,
-				       2);
-		if (ret < 0) {
-			mutex_unlock(&data->mutex);
-			goto err_read;
-		}
-		data->buffer[i++] = raw_val;
-	}
+	ret = regmap_bulk_read(data->regmap, BMC150_ACCEL_REG_XOUT_L,
+			       data->buffer, AXIS_MAX * 2);
 	mutex_unlock(&data->mutex);
+	if (ret < 0)
+		goto err_read;
 
 	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
 					   pf->timestamp);