[PATCH v3 4/8] iio: accel: bmc150: optimize i2c transfers in trigger handler

[Irina Tirdea <irina.tirdea-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

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 i2c 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 i2c bus at each transfer.

Reading all axis values in one i2c transfer reduces the delays
introduced by the i2c bus. Uses i2c_smbus_read_i2c_block_data_or_emulated
that will fallback to reading each axis as a separate word in case i2c
block read is not supported.

Signed-off-by: Irina Tirdea <irina.tirdea-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
 drivers/iio/accel/bmc150-accel.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/iio/accel/bmc150-accel.c b/drivers/iio/accel/bmc150-accel.c
index c6c8416..e686add 100644
--- a/drivers/iio/accel/bmc150-accel.c
+++ b/drivers/iio/accel/bmc150-accel.c
@@ -1082,6 +1082,7 @@ 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						\
@@ -1209,19 +1210,16 @@ 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;
+	int ret;
 
 	mutex_lock(&data->mutex);
-	for (bit = 0; bit < AXIS_MAX; bit++) {
-		ret = i2c_smbus_read_word_data(data->client,
-					       BMC150_ACCEL_AXIS_TO_REG(bit));
-		if (ret < 0) {
-			mutex_unlock(&data->mutex);
-			goto err_read;
-		}
-		data->buffer[i++] = ret;
-	}
+	ret = i2c_smbus_read_i2c_block_data_or_emulated(data->client,
+							BMC150_ACCEL_REG_XOUT_L,
+							AXIS_MAX * 2,
+							(u8 *)data->buffer);
 	mutex_unlock(&data->mutex);
+	if (ret < 0)
+		goto err_read;
 
 	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
 					   data->timestamp);
-- 
1.9.1