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SubjectRe: [PATCH v3 6/8] iio: gyro: bmg160: optimize i2c transfers in trigger handler
On 03/07/15 10:33, Irina Tirdea wrote:
> 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 bmg160 driver does
> one i2c transfer for each axis. This has an impact on the frequency
> of the gyroscope 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@intel.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>

Obviously you'll ideally pick up Ack's from the driver authors /maintainers
as well.

Jonathan
> ---
> drivers/iio/gyro/bmg160.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/iio/gyro/bmg160.c b/drivers/iio/gyro/bmg160.c
> index 4b423f2..04e15e9 100644
> --- a/drivers/iio/gyro/bmg160.c
> +++ b/drivers/iio/gyro/bmg160.c
> @@ -784,6 +784,7 @@ static const struct iio_event_spec bmg160_event = {
> .sign = 's', \
> .realbits = 16, \
> .storagebits = 16, \
> + .endianness = IIO_LE, \
> }, \
> .event_spec = &bmg160_event, \
> .num_event_specs = 1 \
> @@ -822,19 +823,16 @@ static irqreturn_t bmg160_trigger_handler(int irq, void *p)
> struct iio_poll_func *pf = p;
> struct iio_dev *indio_dev = pf->indio_dev;
> struct bmg160_data *data = iio_priv(indio_dev);
> - int bit, ret, i = 0;
> + int ret = 0;
>
> mutex_lock(&data->mutex);
> - for (bit = 0; bit < AXIS_MAX; bit++) {
> - ret = i2c_smbus_read_word_data(data->client,
> - BMG160_AXIS_TO_REG(bit));
> - if (ret < 0) {
> - mutex_unlock(&data->mutex);
> - goto err;
> - }
> - data->buffer[i++] = ret;
> - }
> + ret = i2c_smbus_read_i2c_block_data_or_emulated(data->client,
> + BMG160_REG_XOUT_L,
> + AXIS_MAX * 2,
> + (u8 *)data->buffer);
> mutex_unlock(&data->mutex);
> + if (ret < 0)
> + goto err;
>
> iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> data->timestamp);
>



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