Re: [PATCH v5 6/8] iio: gyro: bmg160: optimize i2c transfers in trigger handler

[Jonathan Cameron <jic23@kernel.org>]

On 12/08/15 15:31, 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>
> Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Note, that in the meantime the bmg160 driver just went all regmap
on us (as part of adding SPI support - though that step hasn't
happened yet).  Hence we'll need a means of telling regmap about this
possibility.

> ---
>  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 b2a6ccb..1ff306d 100644
> --- a/drivers/iio/gyro/bmg160.c
> +++ b/drivers/iio/gyro/bmg160.c
> @@ -772,6 +772,7 @@ 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						\
> @@ -809,19 +810,16 @@ 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,
>  					   pf->timestamp);
>