Re: [PATCH 3/4] iio: imu: inv_mpu6050: skip first sample when gyro is on

[Jonathan Cameron <jic23@jic23.retrosnub.co.uk>]

On Mon, 30 Apr 2018 12:14:10 +0200
Jean-Baptiste Maneyrol <jmaneyrol@invensense.com> wrote:

> Implement generic skip first samples mechanism and use it to
> filter out first sample when gyro is on.
> 
> The problem for these chips is that the first sample of the gyro
> is out of specs, because gyro is not completely stabilized. To
> ensure all data are within sensor specs, we just skip the first
> sample when turning gyro on.
> 
> Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Neat and tidy solution so good.
Is there a similar issue in the read_raw path which seems to just
flick the gyro on then read from it immediately?

I may be missing a delay there which is preventing the data being
bad though.

Jonathan
> ---
>  drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h     | 1 +
>  drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c    | 7 ++++++-
>  drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c | 3 +++
>  3 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h b/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
> index 142a835..dfb9e4e 100644
> --- a/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
> +++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
> @@ -148,6 +148,7 @@ struct inv_mpu6050_state {
>  	struct regmap *map;
>  	int irq;
>  	u8 irq_mask;
> +	unsigned skip_samples;
>  };
>  
>  /*register and associated bit definition*/
> diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
> index e51404f..1b57354 100644
> --- a/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
> +++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
> @@ -185,7 +185,12 @@ irqreturn_t inv_mpu6050_read_fifo(int irq, void *p)
>  		if (result == 0)
>  			timestamp = 0;
>  
> -		iio_push_to_buffers_with_timestamp(indio_dev, data, timestamp);
> +		/* skip first samples if needed */
> +		if (st->skip_samples)
> +			st->skip_samples--;
> +		else
> +			iio_push_to_buffers_with_timestamp(indio_dev, data,
> +							   timestamp);
>  
>  		fifo_count -= bytes_per_datum;
>  	}
> diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c
> index 8a9f869..0d7db27 100644
> --- a/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c
> +++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c
> @@ -49,11 +49,14 @@ static int inv_mpu6050_set_enable(struct iio_dev *indio_dev, bool enable)
>  		if (result)
>  			return result;
>  		inv_scan_query(indio_dev);
> +		st->skip_samples = 0;
>  		if (st->chip_config.gyro_fifo_enable) {
>  			result = inv_mpu6050_switch_engine(st, true,
>  					INV_MPU6050_BIT_PWR_GYRO_STBY);
>  			if (result)
>  				goto error_power_off;
> +			/* gyro first sample is out of specs, skip it */
> +			st->skip_samples = 1;
>  		}
>  		if (st->chip_config.accl_fifo_enable) {
>  			result = inv_mpu6050_switch_engine(st, true,