Re: [PATCH] iio: imu: st_lsm6dsx: discard samples during filters settling time

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On Wed,  8 Feb 2023 15:42:31 +0100
> Lorenzo Bianconi <lorenzo@kernel.org> wrote:
> 
> > During digital filters settling time the driver is expected to drop
> > samples since they can be corrupted. Introduce the capability to drop
> > a given number of samples according to the configured ODR.
> > Add the sample_to_discard data for LSM6DSM sensor.
> > 
> > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> 
> Is this only necessary for the particular sensor you have provided
> values for?  Or is it more general?
> 
> I think the code will currently just set the number of samples to discard
> to 0 for other cases (as no value set for those sensor types).
> That's fine if 0 is definitely the right value for those other sensors.

 I think all the sensors have this information in the datasheet/application
 note. However, even if we add sample_to_discard just for LSM6DSM for the moment,
 we do not introduce any regression for the other sensors with respect to the
 previous codebase since sample_to_discard will be just set to 0 (so we do not
 discard any sample). I can add sample_to_discard for LSM6DSO but at the
 moment I do not have other devices for testing.
 For LSM6DSO, do you prefer to add it in v2 or is it fine a follow-up patch?

 Regards,
 Lorenzo

> 
> Thanks,
> 
> Jonathan
> 
> 
> > ---
> >  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h       | 11 ++++
> >  .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    | 58 +++++++++++++++----
> >  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c  | 18 ++++++
> >  3 files changed, 77 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> > index 499fcf8875b4..8e119d78730b 100644
> > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> > @@ -137,6 +137,13 @@ struct st_lsm6dsx_odr_table_entry {
> >  	int odr_len;
> >  };
> >  
> > +struct st_lsm6dsx_samples_to_discard {
> > +	struct {
> > +		u32 milli_hz;
> > +		u16 samples;
> > +	} val[ST_LSM6DSX_ODR_LIST_SIZE];
> > +};
> > +
> >  struct st_lsm6dsx_fs {
> >  	u32 gain;
> >  	u8 val;
> > @@ -291,6 +298,7 @@ struct st_lsm6dsx_ext_dev_settings {
> >   * @irq_config: interrupts related registers.
> >   * @drdy_mask: register info for data-ready mask (addr + mask).
> >   * @odr_table: Hw sensors odr table (Hz + val).
> > + * @samples_to_discard: Number of samples to discard for filters settling time.
> >   * @fs_table: Hw sensors gain table (gain + val).
> >   * @decimator: List of decimator register info (addr + mask).
> >   * @batch: List of FIFO batching register info (addr + mask).
> > @@ -323,6 +331,7 @@ struct st_lsm6dsx_settings {
> >  	} irq_config;
> >  	struct st_lsm6dsx_reg drdy_mask;
> >  	struct st_lsm6dsx_odr_table_entry odr_table[2];
> > +	struct st_lsm6dsx_samples_to_discard samples_to_discard[2];
> >  	struct st_lsm6dsx_fs_table_entry fs_table[2];
> >  	struct st_lsm6dsx_reg decimator[ST_LSM6DSX_MAX_ID];
> >  	struct st_lsm6dsx_reg batch[ST_LSM6DSX_MAX_ID];
> > @@ -353,6 +362,7 @@ enum st_lsm6dsx_fifo_mode {
> >   * @hw: Pointer to instance of struct st_lsm6dsx_hw.
> >   * @gain: Configured sensor sensitivity.
> >   * @odr: Output data rate of the sensor [Hz].
> > + * @samples_to_discard: Number of samples to discard for filters settling time.
> >   * @watermark: Sensor watermark level.
> >   * @decimator: Sensor decimation factor.
> >   * @sip: Number of samples in a given pattern.
> > @@ -367,6 +377,7 @@ struct st_lsm6dsx_sensor {
> >  	u32 gain;
> >  	u32 odr;
> >  
> > +	u16 samples_to_discard;
> >  	u16 watermark;
> >  	u8 decimator;
> >  	u8 sip;
> > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > index 7dd5205aea5b..c1059a79f5ff 100644
> > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > @@ -457,17 +457,29 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
> >  			}
> >  
> >  			if (gyro_sip > 0 && !(sip % gyro_sensor->decimator)) {
> > -				iio_push_to_buffers_with_timestamp(
> > -					hw->iio_devs[ST_LSM6DSX_ID_GYRO],
> > -					&hw->scan[ST_LSM6DSX_ID_GYRO],
> > -					gyro_sensor->ts_ref + ts);
> > +				/* We need to discards gyro samples during
> 
> Trivial but wrong comment syntax. If that's all that comes up I'll fix it here
> and in other instances below when applying.
> 
> > +				 * filters settling time
> > +				 */
> > +				if (gyro_sensor->samples_to_discard > 0)
> > +					gyro_sensor->samples_to_discard--;
> > +				else
> > +					iio_push_to_buffers_with_timestamp(
> > +						hw->iio_devs[ST_LSM6DSX_ID_GYRO],
> > +						&hw->scan[ST_LSM6DSX_ID_GYRO],
> > +						gyro_sensor->ts_ref + ts);
> >  				gyro_sip--;
> >  			}
> >  			if (acc_sip > 0 && !(sip % acc_sensor->decimator)) {
> > -				iio_push_to_buffers_with_timestamp(
> > -					hw->iio_devs[ST_LSM6DSX_ID_ACC],
> > -					&hw->scan[ST_LSM6DSX_ID_ACC],
> > -					acc_sensor->ts_ref + ts);
> > +				/* We need to discards accel samples during
> > +				 * filters settling time
> > +				 */
> > +				if (acc_sensor->samples_to_discard > 0)
> > +					acc_sensor->samples_to_discard--;
> > +				else
> > +					iio_push_to_buffers_with_timestamp(
> > +						hw->iio_devs[ST_LSM6DSX_ID_ACC],
> > +						&hw->scan[ST_LSM6DSX_ID_ACC],
> > +						acc_sensor->ts_ref + ts);
> >  				acc_sip--;
> >  			}
> >  			if (ext_sip > 0 && !(sip % ext_sensor->decimator)) {
> > @@ -541,8 +553,12 @@ st_lsm6dsx_push_tagged_data(struct st_lsm6dsx_hw *hw, u8 tag,
> >  	}
> >  
> >  	sensor = iio_priv(iio_dev);
> > -	iio_push_to_buffers_with_timestamp(iio_dev, data,
> > -					   ts + sensor->ts_ref);
> > +	/* We need to discards gyro samples during filters settling time */
> > +	if (sensor->samples_to_discard > 0)
> > +		sensor->samples_to_discard--;
> > +	else
> > +		iio_push_to_buffers_with_timestamp(iio_dev, data,
> > +						   ts + sensor->ts_ref);
> >  
> >  	return 0;
> >  }
> > @@ -654,6 +670,25 @@ int st_lsm6dsx_flush_fifo(struct st_lsm6dsx_hw *hw)
> >  	return err;
> >  }
> >  
> > +static void
> > +st_lsm6dsx_update_samples_to_discard(struct st_lsm6dsx_sensor *sensor)
> > +{
> > +	const struct st_lsm6dsx_samples_to_discard *data;
> > +	int i;
> > +
> > +	if (sensor->id != ST_LSM6DSX_ID_GYRO &&
> > +	    sensor->id != ST_LSM6DSX_ID_ACC)
> > +		return;
> > +
> > +	data = &sensor->hw->settings->samples_to_discard[sensor->id];
> > +	for (i = 0; i < ST_LSM6DSX_ODR_LIST_SIZE; i++) {
> > +		if (data->val[i].milli_hz == sensor->odr) {
> > +			sensor->samples_to_discard = data->val[i].samples;
> > +			return;
> > +		}
> > +	}
> > +}
> > +
> >  int st_lsm6dsx_update_fifo(struct st_lsm6dsx_sensor *sensor, bool enable)
> >  {
> >  	struct st_lsm6dsx_hw *hw = sensor->hw;
> > @@ -673,6 +708,9 @@ int st_lsm6dsx_update_fifo(struct st_lsm6dsx_sensor *sensor, bool enable)
> >  			goto out;
> >  	}
> >  
> > +	if (enable)
> > +		st_lsm6dsx_update_samples_to_discard(sensor);
> > +
> >  	err = st_lsm6dsx_device_set_enable(sensor, enable);
> >  	if (err < 0)
> >  		goto out;
> > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > index 3f6060c64f32..966df6ffe874 100644
> > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > @@ -634,6 +634,24 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = {
> >  				.fs_len = 4,
> >  			},
> >  		},
> > +		.samples_to_discard = {
> > +			[ST_LSM6DSX_ID_ACC] = {
> > +				.val[0] = {  12500, 1 },
> > +				.val[1] = {  26000, 1 },
> > +				.val[2] = {  52000, 1 },
> > +				.val[3] = { 104000, 2 },
> > +				.val[4] = { 208000, 2 },
> > +				.val[5] = { 416000, 2 },
> > +			},
> > +			[ST_LSM6DSX_ID_GYRO] = {
> > +				.val[0] = {  12500,  2 },
> > +				.val[1] = {  26000,  5 },
> > +				.val[2] = {  52000,  7 },
> > +				.val[3] = { 104000, 12 },
> > +				.val[4] = { 208000, 20 },
> > +				.val[5] = { 416000, 36 },
> > +			},
> > +		},
> >  		.irq_config = {
> >  			.irq1 = {
> >  				.addr = 0x0d,
> 

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