Re: [PATCH] iio: imu: st_lsm6dsx: add odr calibration feature

Lorenzo Bianconi
2019-10-07T14:07:35Z

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> On LSM6DSO/LSM6DSR/LSM6DSOX/ASM330LHH and ISH330DHCX
> devices it is possible to trim the hardware timestamp
> resolution through the FREQ_FINE[7:0] bits of the
> INTERNAL_FREQ_FINE register, which contains the difference
> in percentage of the effective ODR (and timestamp rate)
> with respect to the typical value.
>
> The formula for calculating the effective ODR reported
> in the application notes has been linearized to the first
> order to simplify the calculation (pls. see note on source
> code).
>
> This change may be useful in the outcome of CTS
> tests regarding the SingleSensorTests and the
> SensorTest#testSensorTimeStamps for high ODRs
>
> Signed-off-by: Mario Tesi <mario.tesi@st.com>

Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>

> ---
> drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h | 4 ++++
> drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c | 5 ++---
> drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c | 23 +++++++++++++++++++++++
> 3 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> index 7485423..9a40587 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> @@ -153,12 +153,14 @@ struct st_lsm6dsx_fifo_ops {
> * @hr_timer: Hw timer resolution register info (addr + mask).
> * @fifo_en: Hw timer FIFO enable register info (addr + mask).
> * @decimator: Hw timer FIFO decimator register info (addr + mask).
> + * @freq_fine: Difference in % of ODR with respect to the typical.
> */
> struct st_lsm6dsx_hw_ts_settings {
> struct st_lsm6dsx_reg timer_en;
> struct st_lsm6dsx_reg hr_timer;
> struct st_lsm6dsx_reg fifo_en;
> struct st_lsm6dsx_reg decimator;
> + u8 freq_fine;
> };
>
> /**
> @@ -344,6 +346,7 @@ struct st_lsm6dsx_sensor {
> * @fifo_mode: FIFO operating mode supported by the device.
> * @suspend_mask: Suspended sensor bitmask.
> * @enable_mask: Enabled sensor bitmask.
> + * @ts_gain: Hw timestamp rate after internal calibration.
> * @ts_sip: Total number of timestamp samples in a given pattern.
> * @sip: Total number of samples (acc/gyro/ts) in a given pattern.
> * @buff: Device read buffer.
> @@ -365,6 +368,7 @@ struct st_lsm6dsx_hw {
> enum st_lsm6dsx_fifo_mode fifo_mode;
> u8 suspend_mask;
> u8 enable_mask;
> + s64 ts_gain;
> u8 ts_sip;
> 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 cabd4bf..d7cacb9 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> @@ -50,7 +50,6 @@
>
> #define ST_LSM6DSX_MAX_FIFO_ODR_VAL 0x08
>
> -#define ST_LSM6DSX_TS_SENSITIVITY 25000UL /* 25us */
> #define ST_LSM6DSX_TS_RESET_VAL 0xaa
>
> struct st_lsm6dsx_decimator_entry {
> @@ -423,7 +422,7 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
> */
> if (!reset_ts && ts >= 0xff0000)
> reset_ts = true;
> - ts *= ST_LSM6DSX_TS_SENSITIVITY;
> + ts *= hw->ts_gain;
>
> offset += ST_LSM6DSX_SAMPLE_SIZE;
> }
> @@ -566,7 +565,7 @@ int st_lsm6dsx_read_tagged_fifo(struct st_lsm6dsx_hw *hw)
> */
> if (!reset_ts && ts >= 0xffff0000)
> reset_ts = true;
> - ts *= ST_LSM6DSX_TS_SENSITIVITY;
> + ts *= hw->ts_gain;
> } else {
> st_lsm6dsx_push_tagged_data(hw, tag, iio_buff,
> ts);
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> index bacc908..2b54ce1 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> @@ -63,6 +63,8 @@
>
> #define ST_LSM6DSX_REG_WHOAMI_ADDR 0x0f
>
> +#define ST_LSM6DSX_TS_SENSITIVITY 25000UL /* 25us */
> +
> static const struct iio_chan_spec st_lsm6dsx_acc_channels[] = {
> ST_LSM6DSX_CHANNEL_ACC(IIO_ACCEL, 0x28, IIO_MOD_X, 0),
> ST_LSM6DSX_CHANNEL_ACC(IIO_ACCEL, 0x2a, IIO_MOD_Y, 1),
> @@ -832,6 +834,7 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = {
> .addr = 0x0a,
> .mask = GENMASK(7, 6),
> },
> + .freq_fine = 0x63,
> },
> .shub_settings = {
> .page_mux = {
> @@ -1020,6 +1023,7 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = {
> .addr = 0x0a,
> .mask = GENMASK(7, 6),
> },
> + .freq_fine = 0x63,
> },
> .event_settings = {
> .enable_reg = {
> @@ -1185,6 +1189,7 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = {
> .addr = 0x0a,
> .mask = GENMASK(7, 6),
> },
> + .freq_fine = 0x63,
> },
> .shub_settings = {
> .page_mux = {
> @@ -1874,6 +1879,24 @@ static int st_lsm6dsx_init_hw_timer(struct st_lsm6dsx_hw *hw)
> if (err < 0)
> return err;
> }
> +
> + /* calibrate timestamp sensitivity */
> + hw->ts_gain = ST_LSM6DSX_TS_SENSITIVITY;
> + if (ts_settings->freq_fine) {
> + err = regmap_read(hw->regmap, ts_settings->freq_fine, &val);
> + if (err < 0)
> + return err;
> +
> + /*
> + * linearize the AN5192 formula:
> + * 1 / (1 + x) ~= 1 - x (Taylor’s Series)
> + * ttrim[s] = 1 / (40000 * (1 + 0.0015 * val))
> + * ttrim[ns] ~= 25000 - 37.5 * val
> + * ttrim[ns] ~= 25000 - (37500 * val) / 1000
> + */
> + hw->ts_gain -= ((s8)val * 37500) / 1000;
> + }
> +
> return 0;
> }
>
> --
> 2.7.4
>

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